GB2243606A - Improvement in or relating to the reduction of halogenated organic compounds. - Google Patents

Abstract

A process for reducing a halogenated aliphatic compound is disclosed which comprises reacting it with a cyclic hydrocarbon which is capable of being converted to an aromatic compound by dehydrogenation, in the liquid phase in the presence of a Group VIII metal hydrogenation catalyst.

Description

IMPROVEMENTS IN OR RELATING TO THE REDUCTION OF HALOGENATED ORGANIC COMPOUNDS This invention relates to the reduction of halogenated organic compounds, and more specifically to the reduction of halogenated aliphatic compounds containing chlorine and fluorine substituents such as chloro-fluoromethanes, -ethanes or propanes.

It is already known, from GB-A-1,578,933, that halogenated ethanes can be reduced by reaction with molecular hydrogen at elevated temperatures and in the presence of an hydrogenation catalyst.

We have now devised an alternative reduction process for halogenated aliphatic compounds such as chlorofluoro-ethanes which has the advantage that it can be carried out continuously in standard equipment and in a liquid phase. The hydrogenation agent can be purified for re-use and the catalyst is inherently kept clean. Since the process is a liquid-phase process it is inherently safer and also involves a lower hydrogen inventory.

In one aspect this invention provides a process for the reduction of a halogenated aliphatic group containing compound wherein the compound is reacted with a cyclic compound, which is capable of being converted to an aromatic compound by dehydrogenation, in the liquid phase and in the presence of a hydrogenation catalyst.

The process of the invention is preferably applied to halogenated aliphatic compounds and, especially, chlorofluoro-ethanes or chlorofluorohydro-ethanes.

The preferred cyclic compound, which does, in effect, behave as a hydrogen-donor, is a cycloalkane or cycloalkene, or an alkyl substituted cycloalkane (or cycloalkene), typically decalin, tetralin, cyclohexane, cyclohexene, or limonene.

The preferred hydrogenation catalyst is a group VIII metal, in general a noble metal/precious metal which can either be used on an inert support e.g. carbon or alumina or in solution as a metal/organic complex. Palladium is the preferred catalyst.

The reaction to which this invention is most applicable is the replacement of a chlorine atom by hydrogen in a chlorofluoroethane, such as 1,1-dichloro-1,2,2,2,- tetrafluoroethane (CC12F.CF3) or in a hydrochlorofluoroethane such as l-chloro-1,2,2,2,-tetrafluoroethane (CHC1F.CF3).

Clearly the hydrogen-donor will be oxidised in the course of the reaction and may be reduced back to its original state in a separate stage.

In general the reaction can be carried out at moderate temperatures (e.g. 2000-3000C) and at moderate pressures (e.g. 200 to 750 psig), so that the reaction occurs principally in the liquid phase, rather than in the gas phase.

The invention will be further illustrated by reference to the following non-limiting Examples.

EXAMPLE 1 Liquid phase preparation of CH2F.CF3 from CHC1F.CF3 A mixture of 20.7 g. (0.15 moles) 1-chloro-1,2,2,2,tetrafluoroethane (CHClF.CF3), 134 g. (0.97 moles) decalin 50:50 mixture cis and trans isomers) and 4.lg.catalyst (5% Pd on charcoal) was charged into an autoclave and heated to 2650C and 242 psig and held under these conditions for 3 hours.

The autoclave was then vented through an aqueous sodium hydroxide scrubber and calcium chloride drying tube and the volatiles were collected in cold traps prior to vacuum transfer. 16.5 g. of material were recovered, with the following analysis: 21.9% CH2F.CF3 (0.035 moles) 2.2% CH3CF3 (0.0004 moles) 0.6% Others 75.3% CHC1F.CF3 (0.091 moles) In addition 0.019 moles of CHC1F.CF3 was recovered from the solvent.

From this data it was calculated that 23% of the CHC1F.CF3 available had been converted to CH2F.CF3. Taking the recovered CHClF.CF3 into account, the CH2F.CF3 had been prepared from CHC1F.CF3 in 87% yield.

EXAMPLES 2 - 7 The process described in Example 1 was repeated using other hydrogen donor solvents, but with the same substrate, CHClF.CF3. The conditions used, and the results obtained, are given in the following Examples.

EXAMPLE DONOR TEMPERATURE PRESSURE REACTION CONVERSION YIELD NO. SOLVENT C PSIG TIME HRS. % % 2 Cyclohexene 265 623 3 10.4 84 3 Cyclohexene 265 614 3 8.7 84 4 Limonene 265 250 3 10.7 73 5 Tetralin 265 297 3 6.5 28 6 cis-Decalin 265 268 3 7.7 28 7 trans-Decalin 265 255 3 34.2 88

Claims (8)

1. A process for reducing a halogenated aliphatic compound which comprises reacting it with a cyclic hydrocarbon which is capable of being converted to an aromatic compound by dehydrogenation, in the liquid phase in the presence of a Group VIII metal hydrogenation catalyst.

2. A process according to claim 1 for reducing a chlorofluoroethane or a chlorofluorohydroethane.

3. A process according to claim 2 wherein the aliphatic compound possesses a perfluoro group.

4. A process according to claim 3 wherein the aliphatic compound is 1-chloro-1,2,2,2-tetrafluoroethane.

5. A process according to anyone of claims 1 to 3 wherein the cyclic hydrocarbon is a cycloalkane or cycloalkene.

6. A process according to claim 5 wherein the cyclic hydrocarbon is decalin, tetralin, cyclohexane, cyclohexene or limonene.

7. A process according to any one of the preceding claims wherein the catalyst is palladium.

8. A process according to any one of the preceding claims which is carried out at a temperature of 200 to 3000C and a pressure of 200 to 750 psig.