METHOD OF FORMING CYCLIC SILOXANE COMPOUNDS FROM

ORGANODIHALOSILANES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62/164087 filed 20 May 2015 under 35 U.S.C. §1 19 (e). U.S. Provisional Patent Application No. 62/164087 is hereby incorporated by reference.

TECHNICAL FIELD

[0002] A method is capable of forming cyclic siloxane compounds from

organodichlorosilanes in the presence of a transition metal on cerium (IV) oxide. The method produces desirable quantities of cyclic trisiloxane compounds.

BACKGROUND

[0003] Cyclic siloxane compounds, such as cyclic trisiloxane compounds, cyclic tetrasiloxane compounds, and cyclic pentasiloxane compounds, are useful as reactants for production of siloxane elastomers. Siloxane elastomers generally have a desirable combination of properties, such as excellent high temperature and weather stability, low temperature flexibility, high compressibility, high electrical resistivity, low dielectric loss, high gas permeability, as well as being odorless. Because of these properties, siloxane elastomers are widely used in industrial and consumer product applications.

Furthermore, octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) offer desirable properties to the personal care market place. These cyclosiloxanes along with some other low molecular weight linear siloxanes offer superior wetting properties combined with a volatility profile that make them useful in the delivery of a variety of personal care products ranging from antiperspirants to shampoo to skin lotions. There is an industry need to produce cyclic siloxane compounds such as cyclic trisiloxane compounds, e.g., hexamethylcyclotrisiloxane (D3).

SUMMARY

[0004] The method described herein forms a product comprising a cyclic siloxane compound. The method comprises: 1 ) combining (a) an organodihalosilane, optionally (b) hydrogen gas, and (c) a transition metal on cerium(IV) oxide catalyst, in a reactor at a temperature of at least 200 °C to form the product. The (a) organodihalosilane has formula R ¹ 2SiX2 , where each R ¹ is independently a hydrogen atom, a hydrocarbyl group, or a halogenated hydrocarbyl group; and each X is independently a halogen atom.

DETAILED DESCRIPTION

[0005] The method described herein produces a product comprising cyclic siloxane compounds. At least a portion of the cyclic siloxane compounds in the product may include cyclic trisiloxane compounds, which are highly strained and typically less stable and more difficult to synthesize than cyclic siloxane compounds with more than three silicon atoms per molecule, such as cyclic tetrasiloxane compounds and cyclic pentasiloxane compounds.

[0006] The cyclic siloxane compound in the product may comprise one or more species, each independently having the formula (R ¹ 2SiO) _n , where each R ¹ is independently a hydrogen atom, a hydrocarbyl group, or a halogenated hydrocarbyl group, and subscript n is at least 3. Alternatively, the hydrocarbyl groups for R ¹ may be independently an alkyl group of 1 to 6 carbon atoms, an alkenyl group of 1 to 6 carbon atoms, or an aryl group of 6 to 10 carbon atoms. Alternatively, the alkyl group may have 1 to 4 carbon atoms. Alternatively, the alkenyl group may have 1 to 4 carbon atoms. Alternatively, the aryl group may have 6 to 8 carbon atoms. Alternatively, the alkyl group may be methyl or ethyl, alternatively each alkyl group may be methyl. Alternatively, the alkenyl group may be vinyl or allyl; alternatively, each alkenyl group may be vinyl.

Alternatively, each aryl group may be phenyl, tolyl or xylyl; alternatively, each aryl group may be phenyl. The halogenated hydrocarbyl groups for R ¹ may be any hydrocarbyl group described above where one or more hydrogen atoms bonded to a carbon atom have been formally replaced with a halogen atom. Halogenated hydrocarbon groups include haloalkyl groups and haloalkenyl groups. Haloalkyl groups include fluorinated alkyl groups such as trifluoromethyl (CF3), fluoromethyl, trifluoroethyl, 2-fluoropropyl,

3,3,3-trifluoropropyl, 4,4,4-trifluorobutyl, 4,4,4,3, 3-pentafluorobutyl, 5,5,5,4,4,3,3- heptafluoropentyl, 6, 6,6,5,5,4,4,3, 3-nonafluorohexyl, and 8,8,8,7,7-pentafluorooctyl; and chlorinated alkyl groups such as chloromethyl and 3-chloropropyl; and halogenated cycloalkyl groups such as fluorinated cycloalkyl groups, e.g., 2,2-difluorocyclopropyl, 2,3- difluorocyclobutyl, 3,4-difluorocyclohexyl, and 3,4-difluoro-5-methylcycloheptyl; and chlorinated cycloalkyl groups such as 2,2-dichlorocyclopropyl, 2,3-dichlorocyclopentyl. Haloalkenyl groups include allyl chloride. Each X is independently a halogen atom, as described above. The halogen atom may be selected from chlorine, bromine or iodine; alternatively chlorine or bromine; alternatively chlorine or iodine. Alternatively, each X may be chlorine. Subscript n is at least 3, alternatively 3 to 9, alternatively 3 to 6, and alternatively 3. The product may optionally further comprise other silicon containing compounds, such as monomeric organohalosilanes and organo-halo-siloxanes.

However, in one embodiment, the product comprises at least 40 mol% of a cyclic trisiloxane compound of formula (R^SiO^. In this embodiment, one instance of may be methyl, and another instance of R ¹ may be selected from hydrogen, methyl, vinyl, and phenyl. For example, the product may include (Me2SiO)3, (MeViSiO)3,

(MeHSiO) ₃ , or (MePhSiO) ₃ .

[0007] The product may further comprise additional silicon containing species. For example, in addition to the cyclic siloxane compounds, silanes of formula R ¹ t>Si ^x (4-b) where subscript b is 0 to 3, and the silane differs from the organodihalosilane (a), and noncyclic polysiloxanes comprising units of formulae

(R ¹ 3SiO)-| /2(R ¹ 2SiO)2/2(R ¹ SiO)3/2 may be formed, where R ¹ is as described above.

[0008] The method described above may further include the steps of providing each of (a) the organodihalosilane, optionally (b) hydrogen gas, and (c) the transition metal on cerium(IV) oxide catalyst before step 1 ). Alternatively, the method may further comprise treating the transition metal on cerium(IV) oxide catalyst before step 1 ). Treating may be performed, for example, by reducing with hydrogen before providing the

organodihalosilane. Each of these starting materials (a), optionally (b), and (c) can be formed and/or provided by any convenient means. Typically, (a) the organodihalosilane is a liquid at room temperature. However, (a) the organodihalosilane may be provided as a gas when used in the method, e.g., through heating to vaporize and/or through the use of a carrier gas. When a carrier gas is used, the carrier gas may be fed through a bubbler that includes (a) the organodihalosilane. The carrier gas may be an inert gas such as argon or nitrogen. Alternatively, the carrier gas may be hydrogen gas (H2) when ingredient (b) is present. The carrier gas may be of any purity but typically has a purity of greater than 90%, alternatively greater than 95%, or alternatively greater than 99%. Inert gases and hydrogen gas is commercially available from, e.g., Praxair.

Typically, (c) the transition metal on cerium (IV) oxide is solid and is provided as particles {i.e., in particulate form). One or more of (a), optionally (b), and/or (c) may be provided in a single amount or may be provided in sequential steps, over a period of time, in a series of smaller amounts. In other words, (a), optionally (b), and (c) may be provided in a first amount and the method further comprise adding a supplemental amount of (a), optionally (b), and/or (c). Supplemental amounts of (a), optionally (b), and/or (c) may be added after the initial step 1 ) of providing and/or combining.

Alternatively, the carrier gas may be excluded from step 1 ) of the method when a liquid organodihalosilane is vaporized at elevated temperatures and the vapor is delivered into the reactor through flow lines which are heated to avoid condensation of the vapor back to liquid. In this embodiment, the vapor is self-carrying.

[0009] The organodihalosilane, (a), has formula R ¹ 2SiX2 , where each R ¹ is independently a hydrogen atom, a hydrocarbyl group, or a halogenated hydrocarbyl group, as described above. The organodihalosilane is exemplified by

methyldichlorosilane (MeHSiC^), dimethyldichlorosilane (Me2SiCl2),

methylvinyldichlorosilane (MeViSiC^), methylphenyldichlorosilane (MePhSiC^), methyldibromosilane (MeHSiB^), dimethyldibromosilane (Me2SiBr2),

methylvinyldibromosilane (MeViSiB^), methylphenyldibromosilane (MePhSiB^), methyldiiodosilane (MeHSil2), dimethyldiiodosilane (Me2Sil2), methylvinyldiiodosilane (MeViSil2), and methylphenyldiiodosilane (MePhSi^). Alternatively, organodihalosilane may be selected from the group consisting of MeHSiCl2, Me2SiCl2, MeViSiCl2, and MePhSiCI ₂ .

[0010] In the method described herein, the product is typically formed in the presence of (c) the transition metal on cerium(IV) oxide also referred to as M/CeC>2, where M represents the transition metal. The transition metal (M) may be Rhenium (Re), Iron (Fe), Nickel (Ni) or Copper (Cu). Alternatively, the transition metal may be Re.

Alternatively, the transition metal may be Fe. Alternatively, the transition metal may be Ni. Alternatively, the transition metal may be Cu. In other words, the cyclic trisiloxane compounds are formed in the presence of the (c) transition metal on cerium (IV) oxide.

[0011] The transition metal on cerium (IV) oxide acts as a catalyst for forming the product. The transition metal is typically disposed on the cerium (IV) oxide, which acts as a solid support for the transition metal. The cerium(IV) oxide may lose oxygen atoms during formation of the product, but can be regenerated by exposure of cerium(lll) oxide to diatomic oxygen (O2) (or atmospheric air) to re-gain an oxygen atom (and reform cerium(IV) oxide), thereby regenerating the catalyst. In addition, any cerium oxychloride (CeOCI) that is produced during formation of the product may also lose chlorine atoms to reform cerium (IV) oxide and also regenerate the catalyst.

[0012] The transition metal on cerium (IV) oxide may be formed by any method known in the art. In one embodiment, the transition metal on cerium (IV) oxide is formed by dissolving a transition metal halide, such as ReCl3, in isopropyl alcohol to form a solution. The solution is then added to Ce02 powder by an incipient wetness technique. The powder is then vacuum dried. Moreover, the particular amount or weight percent of the transition metal on the cerium (IV) oxide is not particularly limited. Typically, the transition metal is present in an amount of 0.01 % to 10%, alternatively 0.1 % to 5%, or alternatively 0.5% to 3%; based on weight of the cerium (IV) oxide. However, these ranges are exemplary, and not limiting. The weight percent of the transition metal on the cerium (IV) oxide may be any value or range of values, both whole and fractional, within those ranges and values described above.

[0013] The method may optionally further include a step of regenerating the cerium (IV) oxide. This may be performed by exposing cerium (III) to diatomic oxygen (O2) and/or to atmospheric air to reform cerium (IV) oxide. Alternatively, this may be performed by treating the cerium oxychloride (CeOCI) such that it loses chlorine atoms to reform cerium (IV) oxide. These steps may occur sequentially or simultaneously and may occur in conjunction with each other or independently.

[0014] In the method described herein, (a), optionally (b), and (c) are combined under conditions sufficient to form a product containing a cyclic siloxane compound, in particular a cyclic trisiloxane compound. The temperature selected depends on various factors including the species of organodihalosilane selected for (a), however, the temperature may be at least 200 °C. Alternatively, the temperature may range from 200 °C to 500 °C, alternatively 350 °C to 500 °C, and alternatively 350 °C to 450 °C.

[0015] The reactor may operate in a continuous, semi-continuous, or batch mode or in a combination of modes. Alternatively, two or more reactors can be used, each independently operating in a continuous, semi-continuous, or batch mode or its own combination of modes. In one example, a first reactor is used to react (a), optionally (b), and (c), and a second reactor is used to generate (and/or regenerate) the cerium (IV) oxide. In this example, one or both of these reactors can be operated in a continuous mode. The particular type of reactor is not limited and may be exemplified by a fluidized bed reactor, a gas phase heterogeneous reactor, or a fixed bed reactor. The length and size of the reactor are also not particularly limited as the reactor may be a laboratory scale reactor or an industrial scale reactor.

[0016] In one embodiment, (c) the transition metal on cerium(IV) oxide is stationary, and (a) the organodihalosilane and when present (b) hydrogen gas are passed through and/or over (c) the transition metal on cerium(IV)oxide. In laboratory scale, (a) the organodihalosilane and/or carrier gas or (b) hydrogen gas typically has a residence time in or over (c) the transition metal on cerium (IV) oxide of 0.1 seconds (s) to 10s, alternatively 0.5s to 10s, alternatively 0.5s to 9.5s, alternatively 1 s to 8.5s, alternatively 1 .5s to 8s, alternatively 2s to 7.5s, alternatively 3s to 7s, alternatively 3.5s to 6.5s, alternatively 4s to 6s, and alternatively 4.5s to 5.5s. An industrial scale reactor or reaction may utilize residence times in similar proportions from those described above or those proportions may be different. It is contemplated that (a) organodihalosilane and when present (b) hydrogen gas can react for a time of from minutes to hours. In other words, the entire reaction (and not any one particular residence time) typically occurs for a time of from minutes to hours. For example, the process may be performed, and (a), optionally (b), and (c) may react, for 1 minute (min) to 60 min, alternatively 1 min to 40 min, alternatively 1 min to 20 min, alternatively, 1 min to 24 hours (h) , alternatively 1 h to 15 h, alternatively, 1 h to 10 h, and alternatively 1 h to 5h hours.

[0017] The pressure at which the method is performed can be sub-atmospheric, atmospheric, or super-atmospheric. For example, the pressure may range from greater than 0 kilopascals absolute (kPa) to 2000 kPa; alternatively 100 kPa to 1000 kPa; and alternatively 101 kPa to 800 kPa.

[0018] The method may optionally further comprise activating the catalyst before step 1 ). Activating the catalyst may be performed by heating the catalyst in the presence of a reducing agent, such as hydrogen, at a temperature greater than 200 °C.

[0019] After step 1 ), the method may optionally further comprise regenerating the catalyst. Regenerating may be performed oxidation and reduction. For example, oxidation may be performed by heating the catalyst in the presence of an oxygen source {e.g., water or air) at a temperature of greater than 200 °C, alternatively 400 °C to 500 °C.

[0020] After step 1 ), the method may optionally further include one or more additional steps after step 1 ). The additional steps may comprise 2) recovering the cyclic siloxane compound from the product. The product may be removed from the reactor before recovering the cyclic siloxane compound. However, one or more of the cyclic siloxane compounds may be removed from the reactor independently from a remainder of the product. One or more of the cyclic siloxane compounds may be recovered from the product by any convenient means, including chromatography, distillation, sublimation, and/or stripping.

EXAMPLES

Reference Example A - Preparation of Re on CeC>2

[0021] Rhenium on cerium (IV) oxide was prepared by incipient wetness impregnation. Rhenium trichloride was dissolved in hydrochloric acid. This solution was added to the CeC>2 until it was just entirely wetted. The wet solid was placed under vacuum for two hours, then heated in an oven for 15 hours at 80°C. The sample (0.844 g, ReCl3 on ceria, 6.3% Re) was loaded into a 6 mm O.D. quartz tube which was fitted into a steel tube flow reactor. The catalyst was reduced with 10 seem H2 at 400 °C for 1 .5 hours, then at 500 °C for 30 minutes. The hydrogen was delivered to the reactor using a Brooks SLA5850 mass flow controller. The heat was supplied by a Thermo Scientific Lindberg Blue Minimite 2.5 cm tube furnace.

Example 1

[0022] The tube from Reference Example A was then heated at 500 °C.

Methyldichlorosilane (MeHSiC^) was placed in a steel bubbler, and 10 seem hydrogen was flowed through the bubbler to carry the hydrogen and MeHSiCl2 vapor into the reactor. The effluent of the reactor was periodically sampled (once every 23 minutes) using a Vici 6-way valve with a 100 uL sample loop. Each sample was sent to an Agilent 7890 GC-MS with thermal conductivity detector for analysis. The reactor temperature was 500°C for 75 minutes (four GC-MS injections), then injections were taken with the reactor at 400 350 °C, and 330 °C. At 500 °C production of silsesquioxanes was favored, and the reactor effluent contained the following selectivities of silicon products: 57 mol% (MeSi03/ ₂ )6, 9 mol% (MeHSiO)3(MeSi03/ ₂ )2, 4 mol% (MeSi03/ ₂ )8, 15 mol% (MeHSiO)4, 10 mol% (Me2SiO)2(MeHSiO)4. At 350 °C cyclic siloxane compounds were the primary products in the reactor effluent. The reactor effluent contained: 58 mol% (MeHSiO)3, 25 mol% (MeHSiO)4, 8 mol% (MeHSiO)5. Conversion of MeHSiCI ₂ was

100% for all injections except the last when the reactor was at 330 °C, where conversion dropped to 69%.

Comparative Example 2 [0023] A reaction of MeHSiCl2 was carried out according to the procedure described in Example 1 . Cerium (IV) oxide that was not doped with any transition metal was used in place of catalyst (c). The temperature of the reactor was started at 200 °C and increased by 50 °C after each GC-MS injection. At 200 ^< € to 300 °C, disiloxanes were the primary products in the reactor effluent. At 250 °C, the reactor effluent contained 34 mol% CIMeHSi-O-SiHMeCI, 32 mol% CIMeHSi-0-SiMeCI ₂ , and 28 mol% MeH ₂ SiCI. No cyclic trisiloxane was detected in the reactor effluent at any temperature.

Example 3

[0024] The procedure described in Example 1 was repeated except using

dimethyldichlorosilane (Me2SiCl2) as the organodihalosilane (a) and 2% Re on CeC>2 as catalyst (c). At 400 °C the reactor effluent for the first 20 minutes of contained: 49 mol% (Me2SiO)3, 21 mol% Me3SiCI, 14 mol% (Me2SiO)4, 7 mol% linear chlorosiloxanes, 4 mol% (Me ₂ SiO)3(Me2Si03/2)2, and 3 mol% (Me2SiO)4_ ₆ (Me ₂ Si03/2)2- Example 4

[0025] The procedure described in Example 1 was repeated except using

methylvinyldichlorosilane (MeViSiC^) as the organodihalosilane (a) and 6.3% Re on CeC>2 as catalyst (c). The temperature in the reactor started at 200 °C and was increased by 50 °C after each GC-MS injection up to 500 °C. A mixture of monomers, linear siloxanes, cyclic siloxanes and silalkylenes were produced at various selectivities depending on the temperature. At 350 °C the reactor effluent contained 39 mol% (MeViSiO)3, 32 mol% EtMeSiCI ₂ , 12 mol% (MeViSiO)4, 8 mol% MeSiCl3, 4 mol%

(MeViSiO)5. At 500 %: the selectivities were 40 mol% EtMeSiCl2, 31 % CIMeViSi-O-

SiViMeCI, 13 mol% MeSiCI ₃ , 5 mol% CI(MeViSiO) ₂ SiMeViCI, 4 mol% (MeViSiO) ₃ , 3 mol% (MeViSiO)4, and 3 mol% CI ₂ MeSi-(CH2)2-SiMeCl2.

Example 5

[0026] The procedure described in Example 1 was repeated except using MeViSiCl2 as the organodihalosilane (a) and 1 .1 % Fe on Ce02 as the catalyst. A mixture of monomers, linear siloxanes, cyclic siloxanes and silalkylenes were produced at various selectivities depending on the temperature. At 350 °C the selectivities were 43% (MeViSiO) ₃ , 15% EtMeSiCI ₂ , 14% (OSiMeVi) ₃ (0 ₃ /2SiMe)2, 7% (OSiMeVi) ₄ (OSiMeCI). Example 6 [0027] The procedure described in Example 1 was repeated except using

methylphenyldichlorosilane (MePhSiC^) as organodihalosilane (a), and 2% Re on cerium(IV) oxide as catalyst (c). The temperature in the reactor started at 200 °C and was increased by 50 °C after each GC-MS injection up to 500 °C. A mixture of monomers, linear siloxanes, cyclic siloxanes and silsesquioxanes were produced at various selectivities depending on the temperature. At 250 °C the reactor effluent contained 79% PhSiCl3 and 21 % (MeSiC>3/2)6- At 350 °C product was 100% CIMePhSi- O-SiPhMeCI. At 450 °C the reactor effluent contained 90% cyclic (MePhSiO)3 and 10% PhSiCI ₃ .

Example 7

[0028] A reaction was carried out between dimethyldichlorosilane (Me2SiCl2) and 2 wt.% copper on cerium (IV) oxide. The Cu/CeC>2 was prepared with the same procedure as Reference Example A. The sample (0.600 g, CuCI ₂ on ceria, 2.0 wt.% Cu) was loaded into the middle of a 12.7 mm O.D. quartz tube which was connected to the gas lines by fluorocarbon polymer compression fittings and mounted into the tube furnace. The catalyst was reduced under a flow of 5 seem H2 and 95 seem Ar at 500 °C for 30 min, and then under a flow of 100 seem of H2 at the same temperature for 2 additional hours. Both H2 and Ar were delivered to the reactor using the Brooks

SLA5850 mass flow controllers. After completion of the reduction step, the catalyst temperature was lowered to 400 °C and the reaction was started by flowing 20 seem H2 through a steel bubbler filled with liquid dimethyldichlorosilane (Me2SiCl2) to carry the vapor to the reactor. During the reaction both the still bubbler with Me2SiCl2 and the reactor with the catalyst were maintained steady at room temperature (23 °C) and at 400 °C, respectively. The effluent of the reaction was samples every 10 minutes using the Vici 6-way valve - Agilent 7890 GC-MS on-line sample analysis system, similar to the one described in the Example 1 . The duration of the reaction was 50 min (6 GC-MS injections). During the course of the reaction the Me2SiCl2 conversion peaked at 10 min at 37.2 mol.% and then steadily declined to 4.6 mol.% at 50 min. At the maximum of the Me2SiCl2 conversion the reaction product distribution was the following: 53 mol.% (Me ₂ SiO)4, 21 mol.% (Me ₂ SiO)3, 1 1 mol.% (Me ₂ SiO)5, 5 mol. % (MeSi03/ ₂ )4, 3 mol.% Me3SiCI, 2 mol.% MeSiCl3, 2 mol.% (Me2SiO)6, and the remainder (3 mol.%) linear methylchlorosiloxanes, primarily Me2CISiOSiMe2CI.

Example 8

[0029] A reaction of Me2SiCl2 and 2 wt.% nickel on cerium (IV) oxide was carried out with the same procedure outlined in Example 7. Unlike the Example 7, the peak Me2SiCl2 conversion (95 mol.%) with the 2 wt.% nickel on cerium(IV) oxide catalyst was observed at beginning of the reaction (first sampling) and the product distribution at this peak activity was the following: 36 mol.% (Me2SiO)4, 35 mol.% (Me2SiO)3, 1 1 mol.% (Me2SiO) ₅ , 8 mol. % (MeSiC>3/2)4, 4 mol.% (Me2SiO)e, 2 mol. % (MeSiC>3/2)3, 1 mol.% Me3SiCI, 1 mol.% MeSiCl3, and the remainder (2 mol.%) linear

methylchlorosiloxanes, primarily Me2CISiOSiMe2CI. The decline of the catalytic activity during the course of the reaction was less pronounced than in comparison with the experiment described in the Example 7. The Me2SiCl2 conversion at 50 min of reaction time with the Ni/CeC>2 catalyst was 54 mol.%.

Example 9

[0030] A reaction of Me2SiCl2 and 2 wt.% iron on cerium (IV) oxide was carried out with the same procedure outlined in the Example 7 and 8. Similar with the Example 8, the peak Me2SiCl2 conversion (73 mol.%) with the 2 wt.% iron on cerium(IV) oxide catalyst was observed at beginning of the reaction (first sampling) and the product distribution at this peak activity was the following: 74 mol.% (Me2SiO)3, 12 mol.%

(Me ₂ SiO)4, 4 mol. % (MeSi03/ ₂ )4, 2 mol. % (MeSi03/ ₂ )3, 2 mol.% (Me ₂ SiO)5, 2 mol.%

Me3SiCI, 2 mol.% MeSiCl3, 1 mol.% (Me2SiO)6 and the remainder (1 mol.%) linear methylchlorosiloxanes, primarily Me2CISiOSiMe2CI.

Example 10

[0031] The procedure described in Example 1 was repeated except using

(trifluoropropyl)methyldichlorosilane [(F3Pr)MeSiCl2] as organodihalosilane (a), and 5 wt.% copper on cerium(IV) oxide as catalyst (c). The temperature in the reactor started at 150 Ό and was increased by 50 °C after each GC-MS injection up to 500 °C. A mixture of monomers, linear siloxanes, cyclic siloxanes and silsesquioxanes were produced at various selectivities depending on the temperature. At 200 °C the reactor effluent contained 57% by area in the TCD analysis (F3PrMeSiO) _n (where n = 3 to 6) cyclic compounds, 14% (F3Pr)MeSiF ₂ , and 6% (F3Pr)MeSiFCI. At 300 °C the reactor effluent contained 67% (F3PrMeSiO) _n cyclic compounds, and 18% monomers [e.g., (F ₃ Pr)MeSiF ₂ ].

Comparative Example 1 1

[0032] A reaction of Me2SiCl2 and 2 wt.% rhenium on titanium oxide was carried out with the same procedure outlined in the Example 7, except the reactor temperature was 500 °C. Conversion of Me2SiCl2 only reached 5 mol.% at the beginning of the reaction, then dropped off. No cyclic siloxane compounds were created; the product distribution in the first injection was the following: 52 mol.% Me3SiCI, 1 1 mol.% MeSiCl3, and 31 mol.% linear methylchlorosiloxanes. This comparative example shows that when a different support is used in place of cerium oxide, cyclic siloxane compounds did not form under the conditions tested.

Example 12

[0033] The procedure described in Example 1 was repeated except using Me2SiCl2 as organodihalosilane (a), 1 .1 wt.% iron on cerium(IV) oxide as catalyst (c), and argon was used as a carrier gas instead of hydrogen. The temperature in the reactor was kept at 400 °C throughout the reaction. The first injection onto the GC-MS at 5 minutes showed 99% conversion of the Me2SiCl2- Product selectivity was as follows: 51 %

(Me2SiO)3, 15% (Me2SiO)4, 4% (Me2SiO)5, 25% branched T-structures [e.g.

(MeSi03/2)2(Me2SiO)3]. This example shows that cyclic siloxanes, including cyclic trisiloxane, can be formed using the method described herein without hydrogen.

Reference Example B

[0034] Rhenium on cerium (IV) oxide was prepared by dissolving 0.1025 g ReCl3

Sigma Aldrich, 99+%) in 8.8 mL of isopropyl alcohol to form a solution. The solution was then added to Ce02 powder by an incipient wetness technique wherein enough solution was added to 2.0679 g Ce02 (Sigma Aldrich, 99%) to just wet the entire mass of powder such that any more solution would not be taken up by the powder. The wet powder was then vacuum dried at 80 °C for 4 hours to yield a powder including 2 wt.% of rhenium on the cerium(IV) oxide powder.

[0035] After formation, 0.60 g of (c) the rhenium on cerium(IV) oxide powder was then loaded into a quartz glass tube and placed in a flow reactor and purged with H2.

Activation of the catalyst was performed with 100 seem H2 (controlled via Omega FMA 5500 mass flow controller) at 500 °C for ~2 hours (heated in a Lindberg/Blue Minimite 1 " tube furnace).

Comparative Example 13

[0036] Reaction was then initiated by bubbling 100 seem of H2 through a stainless steel bubbler containing methyltrichlorosilane (MeSiC^) instead of an

organodihalosilane (a). The temperature in the bubbler was 23°C. The gas and vapor leaving the bubbler were passed into the reactor used in Reference Example B. The bubbler was designed with sufficient contact time such that the MeSiCl3 vapor was in equilibrium with the gases leaving the bubbler, and as such, the flow rate of MeSiCl3 leaving the bubbler could be determined by known thermodynamic relationships. The reactor effluent was periodically sampled over the course of 60 min by GC/GC-MS to monitor the amounts of various reaction products. The effluent of the reactor passed through an actuated 6-way valve (Vici) with constant 100 uL injection loop before being discarded.

[0037] Samples were taken of the reactor effluent by actuating the valve and a 100 uL sample passed directly into an injection port of a 7890A Agilent GC-MS for analysis with a split ratio at the injection port of 100:1 . The GC included two 30 m SPB-Octyl columns (Supelco, 250 urn inner diameter, 0.25 urn thick film), which were disposed in parallel such that the sample was split evenly between the two columns. One column was connected to a thermal conductivity detector for quantification of the reaction products and the other column was connected to a mass spectrometer (Agilent 7895C MSD) for sensitive detection of trace products and positive identification of any products that formed. Instead of being heated in a GC oven, the columns were heated using an Agilent LTM module, i.e., the columns were wrapped with heating elements and thermocouples such that they were precisely and rapidly ramped to desired

temperatures. This low thermal mass system allowed rapid analysis (7 - 10 minutes) between sample injections. The reactor effluent contained no cyclic trisiloxane compounds.

[0038] For purposes of this application, "°C" means degrees Celsius, "cm" means centimeters, "GC" means gas chromatograph, "GC-MS" means gas chromatograph - mass spectrometer, "m" means meters, "Me" means methyl, "mm" means millimeters, "O.D." means outside diameter, "seem" means standard cubic centimeters per minute, "uL" means microliters, and "urn" means micrometers. All amounts, ratios, and percentages recited in the specification are by weight, unless otherwise indicated.

[0039] The Brief Summary of the Invention and the Abstract are hereby incorporated by reference. All ratios, percentages, and other amounts are by weight, unless otherwise indicated. The articles 'a', 'an', and 'the' each refer to one or more, unless otherwise indicated by the context of the specification.

[0040] The disclosure of ranges includes the range itself and also anything subsumed therein, as well as endpoints. For example, disclosure of a range of 2.0 to 4.0 includes not only the range of 2.0 to 4.0, but also 2.1 , 2.3, 3.4, 3.5, and 4.0 individually, as well as any other number subsumed in the range. Furthermore, disclosure of a range of, for example, 2.0 to 4.0 includes the subsets of, for example, 2.1 to 3.5, 2.3 to 3.4, 2.6 to 3.7, and 3.8 to 4.0, as well as any other subset subsumed in the range.

[0041] With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, it is to be appreciated that different, special, and/or unexpected results may be obtained from each member of the respective

Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination with any other member or members of the group, and each member provides adequate support for specific embodiments within the scope of the appended claims. For example, disclosure of the Markush group: alkyl, aryl, and carbocyclic includes the member alkyl individually; the subgroup alkyl and aryl; and any other individual member and subgroup subsumed therein.

[0042] It is also to be understood that any ranges and subranges relied upon in describing various embodiments of the present disclosure independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. The enumerated ranges and subranges sufficiently describe and enable various embodiments of the present disclosure, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range "of 350 to 500" may be further delineated into a lower third, i.e., from 350 to 400, a middle third, i.e., from 400 to 450, and an upper third, i.e., from 450 to 500, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as "at least," "greater than," "less than," "no more than," and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of "at least 0.1 %" inherently includes a subrange from 0.1 % to 35%, a subrange from 10% to 25%, a subrange from 23% to 30%, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. Finally, an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range of "1 to 9" includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1 , which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.

[0043] The subject matter of all combinations of independent and dependent claims, both singly and multiply dependent, is expressly contemplated but is not described in detail for the sake of brevity. The disclosure has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Embodiments of the Invention

[0044] A first embodiment is a method for forming a product comprising a cyclic siloxane compound, where the method comprises:

1 ) combining, at a temperature of at least 200 °C,

(a) an organodihalosilane of formula R ¹ 2SiX2 _> where each R ¹ is independently a hydrogen atom, a halogenated hydrocarbyl group or a hydrocarbyl group; and each X is independently a halogen atom; and

(c) a transition metal on cerium (IV) oxide catalyst, where the transition metal is selected from Rhenium, Iron, Nickel, and Copper;

thereby producing the product comprising the cyclic siloxane compound.

[0045] A second embodiment is the method of the first embodiment, further comprising treating (c) the transition metal on ceirum (IV) oxide catalyst with hydrogen before step

1 )-

[0046] A third embodiment is the method of the first embodiment, further comprising adding (b) hydrogen gas during step 1 ). [0047] A fourth embodiment is the method of the first embodiment, where the cyclic siloxane compound has formula (R ¹ 2SiO) _n where subscript n is 3 to 6.

[0048] A fifth embodiment is the method of the first embodiment, where each is independently hydrogen, alkyl, fluoroalkyl, alkenyl, or aryl; and n is 3 or 4.

[0049] A sixth embodiment is the method of the first embodiment, where one instance of R1 is methyl; and another instance of R^ is hydrogen, trifluoropropyl, methyl, vinyl, or phenyl; and n is 3.

[0050] A seventh embodiment is the method of the first embodiment, where the temperature is 200 °C to 500 °C.

[0051] An eighth embodiment is the method of the first embodiment,, further comprising:

reactivating the catalyst after step 1 ) is completed.

[0052] A ninth embodiment, is the method of the eighth embodiment, where reactivating occurs in a different reactor than a reactor for performing step 1 ).

[0053] A tenth embodiment is the method of the first embodiment, further comprising: adding an additional amount of the rhenium on cerium (IV) oxide after step 1 ).

[0054] An eleventh embodiment is the method of the first embodiment, where step 1 ) is performed continuously in a fluidized bed reactor.

[0055] A twelvth embodiment is the method of the eleventh embodiment, where the reactor is operated at a pressure that exceeds atmospheric pressure.

[0056] A thirteenth embodiment is the method of the twelvth embodiment, further comprising:

removing the product from the reactor.

[0057] A fourteenth embodiment is the method of the first embodiment, further comprising recovering the cyclic siloxane compound from the product.