FIELD OF THE INVENTION

The present invention relates to processes for selective and high yield preparation of 1 , 1 -difluoroethane and more particularly to such successes which comprise contacting chloroethene with hydrogen fluoride in a liquid phase while in the presence of a tin catalyst and an oxygen, nitrogen, or phosphorous-containing additive.

BACKGROUND OF THE INVENTION Komatsu et al., in U.S. Patent No. 4,766,258, disclose a process for the manufacture of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) by allowing hydrochlorocarbons (HCCs) to react with hydrogen fluoride (HF) in the presence of a tin catalyst and an additive chosen from compounds containing oxygen or nitrogen. In most cases, the examples reveal that the additives reduce the activity of the tin catalyst and thus compromise the efficiency of this process towards forming useful yields of higher fluorinated hydrocarbons.

Komatsu et al., in Japanese Kokai publication number SHO 62[1987]-246528, disclose a process for manufacture of HFCs and HCFCs, characterized by allowing a hydrogen-containing halogenated hydrocarbon to react with HF in a liquid phase in the presence of the reaction product from a compound acting as a base in HF, a tin catalyst, and HF. Komatsu teaches the invention in a single example where 1,1,2- trichloroethane is allowed to react with HF in the presence of tin tetrachloride and sodium fluoride. The reaction was carried out as a batch process at 90 to 98°C and 980 kPa for three hours, and the charged mole ratio of reactants was 1,1,2- trichloroethane (16.7) : HF (33.3) : SnCl (1.0) : NaF (1.0). In this example, the isolated product mixture was 32% (wt) 1,2-dichloro-l- fluoroethane (HCFC-141), 1% l-chloro-l,2-difluoroethane (HCFC-142a), and 67% recovered starting material (1,1,2- trichloroethane) with no dimers observed. Based on this single example, all additives discussed in this Kokai publication, used in a process otherwise identical to U.S. Patent No. 4,766,258 issued to these same authors, are proposed to provide similar benefits.

Franklin et al., in U.S. Patent No. 4,968,850, disclose a process for the preparation of HFCs and HCFCs by allowing an unsaturated HCC to react with HF in

a liquid phase in the presence of a tin catalyst and an organophosphorous additive. These additives are described to lead to an efficient halogen exchange process in which the activity of the catalyst used is increased and/or the stability of the additives is improved, and in which few oligomers are formed and the selectivity for worthwhile products is high. However, while exhibiting a decrease in the amount of oligomers formed, the examples reveal a process in which the selectivity for formation of higher fluorinated hydrocarbons is decreased or changed in a negligible manner.

1,1-Difluoroethane, hereinafter referred to as HFC- 152a or 152a, is a compound of considerable utility. It may be used either alone or in blends with other materials as a refrigerant, blowing agent, propellant, cleaning agent, or as an intermediate for other fluorocarbon compounds, such as fluoroethene. HFCs such as HFC- 152a are environmentally acceptable replacements for chlorofluorocarbons (CFCs), since they have no known effect on the earth's stratospheric ozone.

Processes for preparing HFCs and HCFCs from HCCs and HF by metal mediated halogen exchange have found wide industrial utility. The overall process is one in which carbon to chlorine bonds of the HCC are broken and carbon to fluorine bonds are formed in their place. The metal acts in a catalytic capacity leading to a more productive exchange process requiring milder reaction conditions. HFC- 152a has been manufactured in this manner using liquid and gas phase processes. The literature reveals that HFC- 152a has been prepared by allowing chloroethene to react with HF in the presence of salts of various oxidized metals such as tin(IV), titanium(IV), antimony(III), and antimony(V).

Intermediates in the conventional procedures in which HFC- 152a is prepared from chloroethene comprise 1 -chloro- 1 -fluoroethane (HCFC- 151 a, or 151 a) and 1,1- dichloroethane (HCC-150a, or 150a). Byproducts of such conventional procedures include an assortment of oligomeric and polymeric materials; low molecular weight halogenated dimers and oligomers through higher molecular weight halogenated polymers taking the form of oils, tars and dark carbonaceous solids. These byproducts are typically higher molecular weight, e.g., predominately 50,000, with standard weight fraction distribution from 2,000 to 75,000 number averaged molecular weight, branched, polymeric, halogenated hydrocarbons, which may contain metal species acquired from catalyst and other additives, if present. Such higher molecular weight materials can be formed by polymerization of lower molecular weight dimers, trimers, and oligomers with themselves or with the halogenated carbon-containing reagents and their fluorinated adducts. These

byproducts are detrimental to the halogen exchange process as they interfere with catalyst activity, reduce reactor volume, decrease the yield of HFC- 152a, and are a disposal concern.

Modification of the metal catalyst through addition of compounds which are inert to fluorination but reactive with the metal species in HF, leads to catalysts with different properties from the parent. The ideal additive for the exchange process is one which minimizes byproduct formation while enhancing the reaction rate and increasing selectivity towards the desired product.

Conventional processes for making HFC- 152a are undesirable due to the high amounts of tars produced. The inventive process solves the problems associated with conventional processes by reducing the tar formation rates.

SUMMARY OF THE INVENTION

This invention is a process for the selective preparation of HFC- 152a from chloroethene while minimizing formation of oligomeric and polymeric byproducts. The process comprises: providing a liquid phase mixture containing chloroethene, HF, at least one tin catalyst, and at least one compound from the families consisting of oxygen, nitrogen, and phosphorous-containing compounds; heating the mixture; and isolating the HFC- 152a formed.

The reaction components may be charged to a reaction vessel in any order, but preferably, the vessel is first charged with tin catalyst, HF, and the nitrogen, oxygen, or phosphorous-containing additive. The temperature of this mixture is maintained from 20 to 160°C over the reaction period. During this period, chloroethene is added and is converted to 1 -chloro- 1 -fluoroethane (HCFC-151a) under the reaction conditions. This HCFC-151a then undergoes fluorine for chlorine halogen exchange under the reaction conditions and product HFC- 152a distills out of the reaction mixture.

The process of the present invention can be operated as a batch process. It is preferable to operate a continuous process by the continuous addition of HF, tin catalyst, and oxygen, nitrogen, and phosphorous-containing additive to the reaction vessel along with chloroethene accompanied by the removal of HFC-152a and HC1.

Analysis of this process reveals high and selective conversion of chloroethene to HFC- 152a while minimizing the amounts of oligomeric and polymeric byproducts.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 — Schematic of the continuous process used to produce HFC- 152a.

DETAILED DESCRIPTION OF THE INVENTION

This invention is a process for the selective and high yield synthesis of HFC- 152a from chloroethene while minimizing the formation of byproducts. The process comprises: providing a liquid phase mixture comprising chloroethene, HF, at least one tin catalyst, and at least one compound selected from the group consisting of oxygen, nitrogen, and phosphorous-containing compounds, heating the mixture, and isolating the HFC- 152a formed. Results obtained in this study are summarized in Table 1 and reveal the benefits of employing an oxygen, nitrogen, or phosphorous- containing additive in the tin(IV) mediated synthesis of HFC- 152a from chloroethene and HF. Employing the process of the present invention leads to a marked increase in selectivity for formation of HFC-152a over HCFC- 15 la, increased molar yields of HFC- 152a from chloroethene, and decreased amounts of oligomeric and polymeric byproducts.

Table 1 summarizes typical results obtained by employing at least one oxygen, nitrogen, or phosphorous-containing compound in the tin(IV) mediated synthesis of HFC- 152a from chloroethene. Holding all other process variables constant and increasing the mole ratio of nitrogen-containing additive to tin catalyst from about 0 to 6 through the addition of a nitrogen-containing compound causes a corresponding increase in the product HFC-152a/HCFC-151a mole ratio which varies in a non-linear fashion with the amount and exact chemical composition of the nitrogen-containing additive employed. Further, this increase in the mole ratio of nitrogen-containing additive to tin catalyst is accompanied in all cases by a decrease in the mass percent byproducts formed and/or an increase in the molar yield of HFC- 152a. It was also discovered that in the tin (IV) mediated liquid phase synthesis of HFC- 152a from chloroethene, similar such benefits arise when employing an oxygen containing additive such as ethanol (C2H5OH), or a phosphorous-containing additive such as triethyl phosphite (P(OC2H5)3). The synergy of increased HFC- 152a selectivity and increased yield (decreased tar formation), together with the possibility of employing a wide variety of additives, leads to a valuable process.

Tin catalysts for use in the process of the present invention may be selected from the families of tin halides, tin oxyhalides, and organotins. Of the three families, the tin halides are preferred, and of the tin halides, tin(IV) chloride (SnCl4, stannic chloride) is most preferred. Other acceptable tin(IV) halides include SnBr4 and the

series of SnC^F, SnCl2F2, SnClF3, and SnF4; such species as are generated when SnCl4 is allowed to react with HF. Of the tin oxyhalides, compounds such as SnC^O, SnF2θ, and SnClFO are acceptable. For the purpose of the present invention, organotins are compounds in which the tin atom is bonded to from one to four carbon atoms. Organotin compounds such as tetramethyl tin (Sn(CH3)4), oxydiethyl tin (OSn(C2H5)2), and dichlorodimethyl tin (SnCl2(CH3)2) are useful in the process.

The following oxygen, nitrogen, and phosphorous-containing additives may be used alone or in any composition or mixture in the process of the present invention. The nitrogen-containing compounds of the present invention are ammonia (NH3) and nitrogen-containing primary, secondary and tertiary organic compounds such as amines. Examples of acceptable amines include heterocyclic amines such as pyridine, 2-picoline; saturated and unsaturated aliphatic amines such as trimethylamine, triethylamine, sec-butylamine, hexamethylene diamine; aromatic amines such as aniline, toluidine; and triethanolamine, with t-alkyl amines such as trimethylamine and triethylamine being preferred. The oxygen-containing compounds which may be used in the present invention include H2O, H2O2 and other oxygen-generating compounds, and oxygen-containing organic compounds such as alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, sulfones, and epoxy compounds. The oxygen-containing compounds may be poly-oxygenated and may contain unlike oxygenated functional groups selected from hydroxyl, carbonyl, carboxyl, ester, ether, and epoxy groups. Preferred from the family of oxygenated compounds are the aliphatic alcohols such as ethyl alcohol. The phosphorous-containing compounds which may be used in the present invention are selected from the families of organic phosphites, phosphines, and phosphates. Preferred from these families are tri-lower alkyl phosphites such as triethyl phosphite, trimethyl phosphite, tri-n-butyl phosphite, and triisopropyl phosphite; and phenylphosphines such as chlorodiphenylphosphine, and triphenylphosphine oxide.

The quantity of oxygen-containing additive used in the process of the present invention is generally between from about 0.1 mole to 1.5 moles per mole of tin catalyst employed. Preferably, such a process is carried out using between from about 0.6 to 0.9 mole oxygen-containing additive per mole of tin catalyst. The quantity of nitrogen-containing additive used in the process of the present invention is generally between from about 0.1 mole to 6.0 moles per mole of tin catalyst used. Preferably, such a process is carried out using between from about 0.6 to 0.9 mole nitrogen- containing additive per mole of tin catalyst. The quantity of phosphorous-containing additive used in the process according to the invention is generally between from

about 0.05 to 0.5 mole per mole of tin catalyst. Preferably, such a process is carried out using between from about 0.2 mole to 0.35 mole phosphorous-containing additive per mole of tin catalyst.

In one aspect of the present invention, one or more of the aforementioned oxygen, nitrogen, and phosphorous-containing additives and tin catalysts can be combined prior to being contacted with chloroethene. For example, ethanol and SnCl4 can be premixed to form a mixture comprising ethanol/SnCl4. The premixed combination can be employed in any suitable batch or continuous process described herein.

In one aspect of the present invention, the process is performed in a batch operation. Any suitable autoclave, such as a 450 cc Parr ^® Series 4560 Mini Reactor constructed of Hastelloy C ^® can be used. The autoclave is typically fitted with a turbine impeller for agitating the liquid contents of the autoclave, a septum port for introducing or withdrawing liquids from the autoclave by syringe or cannula technique, valved ports for introducing or withdrawing gaseous or liquid materials, a jacketed 0.25 inch diameter tube reflux condenser topped with a valved takeoff port, and an external heating jacket. The inventive batch method generally can be carried out on any scale desired. The equipment and associated feed lines, effluent lines, and associated units should be constructed of materials resistant to HF and HC1. Typical materials of construction, well-known to the fluorination art, include stainless steels and high nickel alloys, such as Monel nickel-copper alloys, Hastelloy nickel-based alloys, and Inconel nickel-chromium alloys.

A dry autoclave is transferred into a dry-box and the desired amount of at least one tin catalyst and at least one compound selected from the group consisting of oxygen, nitrogen, and phosphorous-containing compounds are charged to the autoclave. The tin catalysts are normally loaded into the autoclave while within a dry- box in order to minimize any reaction between the tin compounds and moisture present in the air.

The autoclave is sealed, and removed from the drybox. A port of the autoclave is then attached to a vacuum pump and the lower portion cooled by being placed into liquid nitrogen, and the autoclave is evacuated. By establishing a vacuum in the autoclave, potentially deleterious air is removed thereby permitting more efficient transfer of gaseous HF. Liquid nitrogen facilitates transfer of HF by condensing gaseous HF in the autoclave. The autoclave is then attached to an HF cylinder and the desired amount of HF is vacuum transferred into the autoclave.

The quantities of chloroethene, HF, and tin catalyst present in the autoclave may vary over a broad range of effective operation. The quantity of materials used in the process of the current invention is generally between about 0.1 to at least about 10 (kg chloroethene fed/hour)/kg catalyst, usually about 0.2 (kg chloroethene fed/hour)/kg catalyst when the tin catalyst comprises SnCl4. The initial amount of catalyst charged with HF is generally between about 5 to at least about 35 weight %, for example, SnCl4 in HF, normally from about 10 to about 20 weight % tin catalyst in HF.

After the starting materials are introduced into the sealed autoclave, the autoclave is then detached from the vacuum and HF sources, and allowed to warm to ambient temperature. The autoclave is then heated to a temperature of about 20 to about 160°C, preferably from about 50 to about 95°C, and the total pressure within the autoclave is maintained between about 60 kPa and about 3000 kPa, preferably about 350 kPa. The pressure within the autoclave can be maintained by using any suitable means such as a back-pressure regulator.

Gaseous chloroethene is then added to the autoclave at a rate that varies as a function of the amount of HF and tin catalyst within the autoclave, e.g., adding chloroethene at a rate of about 10 to about 100 seem (about 0.01 to about 0.5 kg/hr/kg-catalyst). A gaseous effluent exiting a reflux condenser, which is in fluid communication with the autoclave, is collected by condensation and monitored. The composition of the effluent is monitored by using an on-line gas chromatograph (GC). After the addition of chloroethene has ceased, the autoclave is vented of excess gaseous and liquid materials by a nitrogen purge. The solid contents of the autoclave are then removed, drowned with water and filtered. The filtrate is rinsed with 10% aqueous hydrochloric acid, water, and dried in a vacuum oven to a constant weight.

The composition of the dried mass is also analyzed in order to determine the amount of tar that is formed.

While the aforementioned batch process can be employed, a continuous process is particularly desirable from an industrial standpoint. Referring now to Figure 1 , Figure 1 is a schematic diagram for a continuous HFC- 152a manufacturing process. A reactor 1 is in fluid communication with a reflux column 2- Typically, the reflux column 2 will have a reflux ratio of between about 2 to about 20 when operated at a pressure of about 340 to about 3000 kPa and a temperature of about 50 to about 150°C. Predetermined amounts (ratios as previously discussed for batch process) of HF, at least one tin catalyst and at least one compound selected from the group consisting of oxygen, nitrogen, and phosphorous-containing compounds are added to

the reactor 1. The contents of the reactor 1 are agitated by using a dual bladed agitator with pump down action 2, heated, and brought to reflux at the desired operating temperature/pressure. When the desired operating conditions have been established, HF and chloroethene are fed continuously to the reactor via one or more feed lines 4. Gas exits from the reactor 1 and is transported to the reflux column 2 via one or more feed lines 5_. The gas stream leaving the reflux column 2 typically consists essentially of HFC- 152a and HC1, e.g., about 60 to about 70 wt % HFC- 152a. A liquid return line £ is connected to the bottom of the reflux column 2- Line 6. returns high boiling intermediates such as 1,1-dichloroethane and HCFC-151a, among others, and any HF to reactor 1. The gas stream leaving the reactor 1 or reflux column 2 can be purified by any suitable manner such as by using two conventional distillation steps (not shown in Figure 1). The first distillation step removes HC1. The second distillation step removes any unreacted intermediates and HF that are recovered and, if desired, recycled to reactor 1.

Similar to operating a batch process as discussed earlier, the continuous production equipment and its associated feed lines, effluent lines and any handling units should be constructed of materials resistant to HF and HC1.

While the previous description has placed particular emphasis upon making a product stream wherein HFC- 152a is the major component, the inventive process can also be operated in a manner which produces other desirable compounds. That is, the inventive process can produce HFC- 152a alone or co-produced with one or more of HCFC- 141 b ( 1 , 1 -dichloro- 1 -fluoroethane), HCFC- 142b ( 1 -chloro- 1,1- difluoroethane), HFC- 143a (1,1-trifluoroethane), among others, e.g., from a hydrochlorocarbon such as 1,1-dichloroethene. The co-produced product can be recovered and employed as a useful mixture, or separated into its individual components.

The following examples are provided for the purpose of further illustrating the present invention without limiting the invention as defined in the appended claims. In the following examples, chloroethene was supplied by Fluka Incorporated, Ronkonkoma, NY. and HF was supplied by Air Products (Allentown, PA.). All compounds employed in the following examples were commercially available.

EXAMPLES

Example I — Triethylamine as Additive

Tin tetrachloride (SnCi4, 37.5 g, 0.144 mol) was added to a Hastelloy C 450 cc Parr Series 4560 Mini Reactor in a dry box. The reactor head, which was equipped with a 0.25 inch diameter tube reflux condenser, was attached then the reactor removed from the drybox and connected to a stainless steel vacuum line. The base of the reactor was immersed in liquid nitrogen and HF (150 g, 7.5 mol) was vacuum transferred into the reactor. The liquid nitrogen cooling bath was removed and triethylamine (N(C2H5)3, 8.71 g, 0.861 mol) was charged to the reactor via syringe through a septum port. The temperature of the reactor was raised using external heating until the internal temperature was near 25°C, and cooling water (3.7°C) was begun circulating through the condenser. A heating jacket was placed around the reactor, and the internal temperature of the reactor was brought to 50°C while maintaining the internal pressure at 350 kPa by use of a back pressure regulator. At this time, flow of chloroethene (50.1 standard cubic centimeter/minute or seem, 8.4 x 10~7 m^/sec) and internal standard methane (9.5 seem, 1.6 x 10 ^" ? m^/sec) were begun. The gaseous effluent was monitored every hour for the 17 hours of chloroethene addition. The molar yield of HFC- 152a based on the chloroethene fed was measured to be 85%. The HFC- 152a was measured by on-line gas chromatography (GC) to be 98% of the effluent. The ratio of HFC-152a/HCFC-151a (averaged from the 4 ^m to the 17 ^m hour of the experiment) measured by GC was 58. At the end of the run, the reactor was vented to atmospheric pressure to drive off volatiles (HF and organics). Further removal of volatiles was assisted by a nitrogen purge. The solids remaining in the autoclave were drowned in water and filtered on a Teflon ^® (PTFE) membrane filter. The filtrate was washed with 10% HCl and then with water and dried in a vacuum oven to constant mass. The tars formed over this run averaged 0.36 g per 100 g chloroethene fed.

Comparative Example 1— No Additive

The apparatus, procedure, and materials used for this comparative example were identical to those disclosed in Example 1 , with the exception that no triethylamine additive was used. The following discussion documents results obtained from this Example and deviations in procedure from that of Example 1.

The HFC- 152a product was measured by on- line gas chromatography to be 98% of the effluent. The ratio of HFC-152a/HCFC-151a (averaged from the 4 ^th to

the 17 ^m hour of the experiment) was measured to be 40. After 18 hours of operation, the reaction was stopped and worked-up as in Example 1. The tars formed over this run averaged 2.30 g per 100 g chloroethene fed.

Table 1 — Examples 1 thr ugh 15 and Comparative Examples . through 3.

Examples 2 through 13 employed a procedure substantially identical to that disclosed in Example 1 , and Comparative Example 2 employed a procedure substantially identical to Comparative Example 1. The reaction products and process variables which were altered or varied from the standard procedure of Example 1 are reported in Table 1. Process variables which remained constant throughout the runs are listed in the Note following Table 1.

1ΔBL I

Oxygen. Nitrogen, and Phosphorous-Containing Additives

Product Grams Tar

Mole % Mole per 100 g

Additive (moles used, mole Reaction Yield Ratio Chloroethene

Ex. ^a ratio to tin catalyst) Time (hr) 152a 152a/151a Fed

Cl None 18 85 40 2.30

C2 None 16.3 87 44 2.03

1 N(C ₂ H ₅ ) ₃ (0.86, 6.0) 17 85 58 0.36

2 N(C ₂ H ₅ ) ₃ x3HF (0.864, 6.0 16 97 76 0.45 )

3 N(C ₂ H ₅ ) ₃ 16 89 52 0.57 (0.043, 0.30)

4 N(C ₂ H ₅ ) ₃ 15 84 41 0.29 (0.144, 1.0)

5 2-methyl pyridine 16 87 69 0.56 (2-picoline) (0.086, 0.60)

6 P(OC ₂ H ₅ ) ₃ (0.437, 3.0) 16 84 50 0.13

7 P(OC ₂ H ₅ ) ₃ (0.087, 0.60) 14 83 28 0.05

8 C ₂ H ₅ OH (0.13, 0.90) 14 88 55 0.14

9 2-propanone (acetone) 16 87 63 0.49 (0.144, 1.0)

10 N(CH ₃ ) ₃ (0.096, 0.67) 16.5 89 75 0.49

1 1 N(CH ₃ ) ₃ (0.144, 1.0) 16.3 87 50 0.30

12 NH(C ₂ H ₅ ) ₂ (0.144, 1.0) 16.5 90 66 0.14

13 tetramethylene sulfone 15.8 85 91 0.74 (0.144, 1.0)

Table 1 Notes a: As in Example 1, Examples 2-13, Cl, and C2 used 0.144 mole SnCl4, 7.5 moles HF, and were carried out at 50°C and 350 kPa.

b: These examples employed 0.383 mole SnCi4, 15 moles HF, and the reactions were carried out at 80°C. See following detailed procedural description for Examples 14, 15, and C3.

Example — Ethanol as Additive

Tin tetrachloride (SnCLj., 100. g, 0.383 mol) and potassium fluoride (KF, 13.4 g, 0.230 mol) were charged to a Hastelloy C ^® 600 cc Parr ^® Mini Reactor in a dry box. The reactor head was equipped with two ports for feed or sampling, a reflux column with port for collection of exiting vapors, and an agitator. The reactor was sealed, the base cooled, and HF (300 g, 15 mol) followed by ethanol (5.3 g, 0.12 mol) were charged to the reactor. The resulting liquid mixture was allowed to sit for 15 hours. The contents of the reactor were then heated to 80°C and agitation and chloroethene feed begun. HF feed was then started and adjusted so as to maintain a constant total weight of material in the reactor. Once this was attained, and once successive on-line GC analyses of the reflux condenser effluent were within experimental error, the process was consider to be at steady state. At a 19.6 g/hr (0.31 mol/hr) rate of chloroethene feed, the following steady state results were obtained by on-line GC analysis of the reflux condenser effluent: HFC- 152a (96.7% by GC peak area integration), chloroethene (0.04%), HCFC-151a (2.2%), 1.1 -dichloroethane (0.5%). The relative ratio of HFC-152a/HCFC-151a was measured by GC to be 44. At the end of the run. the reaction mixture was worked up by the procedure of Example 1. The tars formed over this run averaged 4.6 g per 100 g of chloroethene fed.

Example 15 — Ethanol Additive

The apparatus, procedure, and materials used for this example were identical to those discussed for Example 14. The following discussion documents results obtained from this example and deviations in procedure from Example 14. The ethanol charge was 10.6 g (0.23 mol). At a 19.6 g/hr (0.31 mol/hr) rate of chloroethene feed, the following steady state results were obtained by on-line GC analysis of the reflux condenser effluent: HFC- 152a (95.2% by GC peak area integration), chloroethene (0.0%), HCFC-151a (3.9%), 1,1 -dichloroethane (1.0%). The relative ratio of HFC-152a/HCFC-151a was measured by GC to be 24. At the end of the run the mixture was worked up by the procedure of Example 1. The tars formed over this run averaged 4.6 g per 100 g of chloroethene fed.

Comparative Example 3 - No Additive

The apparatus, procedure, and materials used for this example were identical to those discussed for Example 14, except that no ethanol additive was employed. The following discussion documents results obtained from this example and deviations in procedure from Example 14.

The SnCl4 charge was 140 g (0.54 mol) and the reaction was carried out at 76°C. At a 18.2 g/hr (0.29 mol/hr) rate of chloroethene feed, the following steady state results were obtained by on-line GC analysis of the reflux condenser effluent: HFC- 152a (89.6% by GC peak area integration), chloroethene (0.0%), HCFC- 151a (7.8%), 1 , 1 -dichloroethane (2.4%). The relative ratio of HFC- 152a/HCFC- 151 a was found by GC to be 1 1. At the end of the run the mixture was worked up by the procedure of Example 1. The tars formed over this run averaged 7.1 g per 100 g of chloroethene fed.