The reluctance of branched chain ketones to react with hydroxyl a ine is well known in the art. The rate of oximation of over 200 ketones was determined by Kletzke, J. Chem. Eng. Data, 1973, 18, 93 and J. Org. Chem. , 1964, 29, 1363, and shown to be dependent on a variety of structural factors. Kletzke's work showed that oximation of diisobutyl ketone (2,6—dimethyl—4— heptanone) is 600 times slower than the corresponding reaction of 2—pentanone, while diisopropyl ketone (2,4— dimethyl—3—pentanone) is fully 2600 times slower. The preparation of oximes typically involves addition of an aqueous base to a bi—phasic mixture of ketone and aqueous hydroxylamine using a co—solvent such as ethanol as is disclosed by Sandier and Karo, "Organic Functional Group Preparations", Vol. 3, pp. 372-381, Academic Press, New York, 1972. Among the bases used are aqueous solutions of sodium hydroxide (Buck et al, Org. Syn. Coll. Vol II, p. 622; Schoenewaldt et al, J. Org. Chem. 1968, 33, 4270) or sodium carbonate (Bousquet, Org. Syn. Coll. Vol II, p. 313). Another method of preparation involves the portion-wise addition of powdered sodium hydroxide to a reaction mixture which contains both

organic and aqueous phases (Lachman, Org. Syn. Coll Vol II, p. 70).

Autrey et al, J. Am. Chem. Soc. 1968, 90, 4924, have reported the preparation of the ketoxime of tetralone by the addition of powdered sodium hydroxide to a reaction mixture containing alcohol, hydroxylamine hydrochloride and the ketone in the absence of water. Another method, reported by Pearson et al, J. Org. Chem. 1963, 28, 1557, for the preparation of highly hindered oximes involves the reaction of a ketone and hydroxyl¬ amine source with a mixture of 2—methyl—2—butanol/ potassium 2—methyl—2—butoxide at room temperature over several months time. Pearson et al note that the reaction can not be accelerated by heating due to competing decomposition of the hydroxyl amine. The reaction of hindered ketones with hydroxylamine at 9500 atmospheres pressure has been reported by Jones et al, J. Am. Chem. Soc. 81, 1959, 2151.

I have discovered that ketoximes, especially oximes of branched chain ketones, can be prepared in good yields at satisfactory rates by contacting a ketone with a hydroxylamine salt in the presence of an alkanol solvent and a heterogeneous carbonate base under essentially anhydrous conditions. The total absence of water not only is not critical but minor amounts of water, e.g., up to 5 weight percent, based on the weight of the alkanol, has been found to enhance reaction rates. The presence of such minor amounts of water is particularly advantageous in the practice of the process on an industrial scale since the water/alkanol mixture is less flammable than the anhydrous alkanol.. The products obtained from this embodiment of my invention are of adequate purity and low enough color to be used

in subsequent reactions after a solvent stripping operation. The process, in general, also is advantageous in that no dramatic temperature increases (exotherms) , which are especially troublesome in commercial operations, occur during the practice of the process.

The ketoxime products of my novel process are particularly useful in the manufacture of blocked isocyanate compounds which are used extensively in thermosetting coating formulations, particularly powder coating compositions. Ketoximes also are used as chemical intermediates for a variety of agrichemical and pharmaceutical applications, as antiskinning aids in paints and in silicone sealants. The process provided by this invention may be used to prepare the oximes of dialkyl ketones (alkanones) having 5 to 20 carbon atoms. However, the advantages inherent in the process render the process particularly useful for the preparation of oximes of branched chain (hindered) alkanones having 7 to 20 carbon atoms wherein the branching occurs at both carbon atoms a or b relative to the ketone carbonyl. Such branched chain ketones may be characterized by the formula

wherein R ¹ and R ³ are independently selected from hydrogen and alkyl of up to 6 carbon atoms; each R ² is hydrogen or alkyl of up to 3 carbon atoms, especially methyl; m and n each is 0 or 1; and the sum of m + n =

2, provided that the alkanones are branched chain, e.g., when R ¹ = R ² = hydrogen, each m = 1. Examples of such alkanones include 2,4—dimethyl—3—pentanone (diisopropyl ketone) and 2,6-dimethyl—4—heptanone (diisobutyl ketone) .

The alkanol reaction medium consists of 1 or more alkanols of up to 4 carbon atoms with ethanol and 1— and 2—propanol being particularly suitable. The amount of alkanol is not a critical element of my invention and can be varied substantially depending, for example, on the materials and equipment used in the process. Typically, the amount of alkanol used will give an alkanol:ketone weight ratio in the range of 0.3:1 to 3:1, preferably 0.6:1 to 2.2:1. As noted above, the alkanol solvent may contain, and preferably contains, up to 5 weight percent, based on the weight of the alkanol, water, e.g., from about 3 to 5 weight percent.

The hydroxylamine salt used may be any compound which provides hydroxylamine in the practice of the process. Hydroxylamine hydrochloride and hydroxylamine sulfate are readily available salts and therefore represent the preferred hydroxylamine salts. The amount of the hydroxylamine salt employed may vary considerably, depending on various factors such as the amount of alkanol present, the equipment utilized, etc. To achieve reasonable production rates, the hydroxyl¬ amine salt normally is used in an amount of 0.6:1 to 1.5:1, preferably 0.8:1 to 1.1:1, equivalents of hydroxylamine salt per mole of ketone reactant. The carbonate base compound required by the process of the present invention may be any compound which will convert the hydroxylamine salt to hydroxylamine under

the conditions and in the presence of the alkanols and ketones employed in the process. Examples of such carbonate base compounds include the alkali and alkaline earth carbonates and bicarbonates. The alkali bicarbonates and, particularly, carbonates, especially sodium and potassium carbonate, are the preferred carbonate base compounds. These carbonate compounds typically are used in an amount of 0.8 to 2, preferably 1.0 to 1.6, equivalents of carbonate base compound per mole of the hydroxylamine salt.

The process provided herein may be carried out at a temperature in the range of 15 to 120°C at atmospheric pressure or moderately elevated pressures, e.g., to achieve a reaction temperature higher than the atmospheric boiling point of the reaction mixture. The process preferably is carried out at a temperature of 65°C up to the boiling point of the reaction mixture, e.g. , up to 110°C.

The present invention also includes a process for the preparation of certain blocked polyisocyanate compounds, i.e., adducts of one or more ketoximes and one or more polyisocyanate compounds, utilizing the process described hereinabove. This embodiment of my invention comprises the steps of: (1) contacting a ketone with a hydroxylamine salt in the presence of an alkanol solvent and a heterogenous carbonate base under essentially anhydrous conditions to form a ketoxime of the ketone; (2) reacting the ketoxime with a polyisocyanate compound to obtain the adduct of the ketoxime and the polyisocyanate compound.

The first step of the two—step process is described in detail hereinabove.

The second step of the process is carried out in the absence of any significant amount, e.g., not more than 5 weight percent, preferably not more than 0.5 weight percent based on the weight of the ketoxime, of any compounds which are reactive with the isocyanato group. Thus, all or substantially all of the alcohol and water, if any, present in the reaction mixture obtained from the first step is separated, for example, by distillation under vacuum, from the ketoxime. In practice, it is preferred to add to the reaction mixture obtained from the first step sufficient water to dissolve the salts, comprising the salt residue of the hydroxylamine salt and any remaining heterogenous carbonate base, and form a two—phase system. The organic phase containing the ketoxime and most of any unreacted ketone present may be submitted to a vacuum distillation to remove alkanol and water. The second step may be carried out by adding a polyisocyanate compound to the crude product of step (1) after all, or essentially all, of the alkanol and water have been removed therefrom. The reaction of the ketoxime and the polyisocyanate compound typically is conducted at a temperature in the range of 20 to 100°C.

Optionally, the second step may include an inert solvent such as a hydrocarbon, e.g., heptane, xylene and toluene; a halogenated hydrocarbon, e.g., methylene chloride and chlorobenzene; an ether, e.g., dioxane and tetrahydrofuran; an alkyl carboxylate ester, e.g., C,—C ₄ alkyl acetates such as ethyl and butyl acetate; or a

mixture of such inert solvents. The second step also may be carried out in the presence of a catalyst selected from tertiary amines and organo—tin compounds. Examples of the tertiary amines include trialkyl amines, e*»g«, having a total carbon content of up to 60 carbon atoms, preferably up to 12 carbon atoms, and heterocyclic amines such as N—alkylpiperidine, N— alkylmorpholine, 1,4-diazabicyclo[2.2.2]octane, pyridine, N—alkyli idazole and the like. Examples of the organo—tin catalysts include dialkyltin dicarboxylates such as dibutyltin dilaurate and dibutyltin dimaleate, dialkyltin oxides such as dibutyltin oxide, tin carboxylates such as stannous octanoate and dialkanoyloxy-tetraalkyl—distanoxanes such as 1,3—diacetoxy—1,1,3,3—tetrabutyldistanoxane.

The polyisocyanate compounds useful in the two—step embodiment of my invention include aliphatic, cyclo— aliphatic and aromatic compounds which contain at least two isocyanato groups and are capable of cross—linking coating compositions, e.g., thermosetting coating compositions wherein the polymeric resin or binder contains chain—terminating and/or pendant hydroxyl groups. Examples of the polyisocyanate compounds include hexamethylene diisocyanate, isophorone di— isocyanate, methylene—bis(cyclohexylisocyanate) , toluene diisocyanate and bis(1—isocyanato—1-methy1ethyl)benzene. The preferred diisocyanates comprise methylene-bis— (cyclohexylisocyanate) , bis(1—isocyanato—1—methylethyl)— benzene and isophorone diisocyanate. The material commonly referred to as isophorone diisocyanate may consist primarily of the difunctional, monomeric isophorone diisocyanate, i.e., a mixture of the cis and trans isomers of 3—isocyanatomethyl—3,5,5—

trimethylcyclohexylisocyanate, the difunctional dimer thereof, the trifunctional trimer thereof or a mixture of the monomeric, dimeric and/or trimeric forms. For example, the polyisocyanate compound used may be a mixture consisting primarily of the difunctional, monomeric isophorone diisocyanate and the trifunctional trimer of isophorone diisocyanate. The trimer of isophorone diisocyanate, i.e., mixed isomers of triisocyanato cyclic isocyanurate, is described in U.S. Patent 4,150,211. The preferred ketoxime—polyisocyanate adducts which may be prepared according to the process described herein are comprised of polyisocyanate compounds wherein the isocyanato groups have been converted to groups having the formula

wherein R ¹ , R ² , R ³ , m and n are defined hereinabove. The preferred polyisocyanate compounds consist of the above- described monomeric, dimeric and trimeric forms of isophorone diisocyanate, methylene—bis(4,4'—cyclohexyl— isocyanate) and 1,3— and 1,4—bis(1—isocyanato—1— methylethyl)benzene.

The processes provided by the present invention are further illustrated by the following examples. Each oximation reaction was monitored by periodically removing samples from the reaction mixture, extracting the mixture with water/methylene chloride and analyzing the resulting organic phase by gas chromatography (GC) .

Analyses were conducted using a 30 m x 0.25 mm DB-5 capillary column on a Hewlett-Packard HP-5890 gas chromatograph equipped with a flame ionization detector, an HP-3393A integrator, and an HP 7673A autoinjector. In each of the following examples the hours of elapsed time (Time) at the time of the removal of each sample is given along with the GC area percents for the ketone reactant (Ketone) employed and the oxime product (Oxime) produced. Elapsed reaction time commenced at the time all reagents were combined unless otherwise noted.

For reactions of isocyanates with oximes, reaction progress was determined by infra—red analysis of the characteristic isocyanate absorption at ca. 2230— 2260 cm" ¹ . The 2,6—dimethyl—4—heptanone used in the reactions was obtained by the distillation of a commercial grade of 2,6—dimethyl—4—heptanone, which is a mixture of 2,6— dimethyl—4—heptanone and 4,6—dimethyl—2—heptanone to obtain the 2,6-dimethy1—4—heptanone isomer in 95—99% purity. The spectral data for 2,6—dimethyl— 4—heptanone oxime (DMHO) and 2, -dimethyl—3-pentanone oxime (DMPO) are listed in Table 1. EXAMPLE 1 In a 3—neck, 1—L flask equipped with a mechanical stirrer, condenser, nitrogen inlet and thermocouple temperature regulator was placed 2,6—dimethyl—4— heptanone (176.7 g; 1.243 mol) , hydroxyl amine sulfate (101.7 g; 0.620 mol, 1.24 equivalents) and ethanol (200 mL) . The solution was warmed to 40°C and sodium carbonate (68.95 g; 0.651 mole; 1.301 equivalents) was added portion—wise. After the addition was complete the

solution was warmed to reflux (approximately 95°C) and the reaction progress was determined by GC.

Time

0.75 2.75

6.00

10.00

25.50

After 27.0 hours, the reaction mixture was cooled to room temperature, 200 mL water were added and the layers separated. The organic phase was washed with brine, concentrated in vacuo, and distilled to give 139.8 g (72% of theory) 2,6—dimethyl—4—heptanone oxime. EXAMPLE 2 In a 1—L, 3—neck flask equipped with a mechanical stirrer, condenser, nitrogen inlet and thermocouple temperature regulator was placed 2—propanol (172 mL) hydroxylamine sulfate (93.13 g; 0.568 mol, 1.136 equivalents) and 2,6—dimethy1—4—heptanone (164.14 g (1.154 mol). The solution was vigorously stirred and sodium carbonate (63.2 g; 0.596 moles; 1.193 equivalents) was added. After 1.5 hours, the solution was warmed to reflux (99°C) . The progress of the reaction was as follows:

After 30 hours, the reaction was cooled to room temperature, 150 mL water were added and the layers separated. The organic layer was washed with brine and

distilled to give 139.85 g (79% of theory) 2,6—dimethy1- 4—heptanone oxime. EXAMPLE 3

This example illustrates the advantages of inclusion of a minor amount of water in the reaction mixture with i—propanol solvent.

In a 1—L, 3—neck flask equipped with a mechanical stirrer, condenser, thermocouple temperature regulator and nitrogen inlet was placed 2 ,6-dimethy1—4—heptanone (163.4 g; 1.149 mol) , hydroxylamine sulfate (93.2 g; 0.568 mol, 1.136 equivalents), 2—propanol (172 mL) , water (10 mL) and sodium carbonate (63.2 g; 0.596 moles, 1.193 equivalents). The solution was heated to reflux (approximately 97°C) and the extent of reaction determined by GC.

The reaction mixture was cooled to room temperature after 22 hours and 150 mL water were added and the layers separated. The organic layer was washed with brine and distilled as before to give 157.8 g (88.5% of theory) of 2,6—dimethyl—4—heptanone oxime.

EXAMPLE 4 This example illustrates the preparation of 2,6-di- methyl—4—heptanone oxime and subsequent direct use of the material in the preparation of a blocked isocyanate.

In a 2—L, 3—neck flask equipped with a mechanical stirrer, nitrogen inlet, thermocouple temperature regulator and condenser was placed 2 ,6—dimethyl—4— heptanone (376.8 g; 2.65 mol), 2—propanol (360 mL) and water (21 mL) . The solution was warmed to 50°C at which point hydroxylamine sulfate (206.86 g; 1.26 mol, 2.52 equivalents) was added. Heating was continued to 70°C and sodium carbonate (135.6 g; 1.279 moles; 2.559 equivalents) was added. Some effervescence was noted at this point. The solution was heated further to 85°C and maintained at that temperature for 8 hours, after which time 400 mL water were added and the solution was allowed to cool to room temperature. The resulting two phases were separated and washed as described in the preceding examples, the organic phase was filtered through a small pad of filter aid and the solvent was removed at 30-32 torr. Analysis of the resulting crude product by GC (mass 312.6 g) showed it contained 7.5 area percent ketone reactant and 90.1 area percent oxime product. This crude oxime was dissolved in 150 mL methylene chloride and 5 mL triethyl amine. To this solution was added 1,3—bis(1—isocyanato—1— methylethyl)benzene (184 mL; 0.791 mol) dropwise at such a rate as to keep the temperature below 35°C. The solution was subsequently warmed to 55°C and maintained at that temperature for 40 minutes at which point infra¬ red spectroscopy showed no remaining isocyanate. The warm solution was poured into an Erlenmeyer flask and recrystallized from petroleum ether—acetone to yield 356.9 g (81% of theory) of the blocked diisocyanate, the adduct of 2,6—dimethyl—4—heptanone oxime and 1,3—bis(1— isocyanato—1—methylethyl)benzene.

EXAMPLE 5

In a 1—L, 3-neck flask equipped with a mechanical stirrer, nitrogen inlet, reflux condenser and thermo¬ couple temperature regulator was placed 2,4—dimethyl-3- pentanone (201.5 g, 1.764 mol), ethanol (100 mL) and hydroxylamine hydrochloride (129.2 g; 1.859 mol, 1.859 equivalents) . The solution was warmed to 38°C and sodium carbonate (120.7 g; 1.139 moles; 2.278 equivalents) was added portion—wise and subsequently heated further to 70°C. The reaction progress was: Time Ketone Oxime 4.0 52.4 41.9

6.0 16.6 78.9

After 6 hours reaction time, the solution was allowed to cool to room temperature, 350 mL water and 100 mL methylene chloride were added and the layers separated. The organic phase was washed with brine, concentrated in vacuo and crystallized from the melt to give 159.9 g (70% of theory) 2,4-dimethyl-3-pentanone oxime.

COMPARATIVE EXAMPLE 1

In a 500-mL, 3-neck flask equipped with a magnetic stirrer, nitrogen inlet, thermometer and reflux condenser was placed 2,6—dimethy1— 4—heptanone(100 mL; 79 g; 0.556 mol), water (156 ml) water and hydroxylamine sulfate (44.08 g; 0.269 mol; [NH ₂ OH] ₂ H ₂ S0 ₄ ) . The solution was cooled in an ice—bath and a solution of sodium hydroxide (24.1 g in 25 L water) was added drop¬ wise at such a rate as to keep the temperature below 30°C (approximately 45 minutes) . The solution pH after the addition was 13—14. The solution was allowed to warm to room temperature and stirred for 14 hours at that temperature. After this point gas chromatography

indicated that the organic phase consisted of 95.9% of the ketone reactant and only 0.9% oxime product. The solution was warmed to and maintained at 78—90°C and the progress of the reaction was determined by GC.

After 137.5 hours, the solution was cooled to room temperature, the layers were separated and the organic phase washed with brine. The organic layer was concentrated in vacuo and vacuum distilled at 85°C/1 torr to give 45.35 g (54% of theory) of 2,6—dimethyl—4— heptanone oxime. This example illustrates the extremely poor reaction rate when 2,6-dimethy1-4—heptanone oxime is prepared in aqueous reaction medium using sodium hydroxide according to known procedures.

COMPARATIVE EXAMPLE 2

In a 500—mL, 3—neck flask equipped with a mechanical stirrer, addition funnel, and thermocouple- regulated heating mantle was placed 2,6—dimethyl—4- heptanone (89.2 g; 0.627 mol), ethanol (25 L) and a solution of hydroxylamine sulfate (52 g; 0.317 mol,

0.634 equivalents) in water (79 mL) . The solution was stirred and a solution of sodium hydroxide (25.8 g; 0.645 moles) in water (30 mL) was added drop—wise at

such a rate as to keep the temperature below 46° (approximately 30 minutes) . The solution was heated to reflux (99°C) after addition of the sodium hydroxide solution and the reaction progress determined.

After 28 hours, the crude reaction mixture was cooled to room temperature and the reaction mixture worked—up as described in the preceding example to give 71.1 g (72.2% of theory) 2,6—dimethyl—4—heptanone.

TABLE I ^■ H NMR Data for DMHO and DMPO DMHO fid. fm.#H'sn DMPO ( ■d. (m.#H's) ) 0.91 (d,6H) 1.13 (d,6H)

0.94 (d,6H) 1.18 (d,6H)

1.82-1.95 (m,lH) 2.50-2.64 (m,lH)

1.96-2.04 (m,lH) 3.12-3.28 (m,lH)

2.04 (d,2H) 2.24 (d,2H)

The invention has been described in detail with particular reference to preferred embodiments thereof. However, it will be understood that variations and modifications may be effected within the spirit and scope of the invention.