Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2000-05-26
2001-08-14
Wong, Edna (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
Reexamination Certificate
active
06274005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hexafluoroacetone and a method of preparation for same.
2. Description of Related Art
Many organic compounds which are polyfluorinated or perfluorinated are quite valuable. Some of the many uses of one such simple perfluorinated ketone, hexafluoroacetone [HFA], were reviewed a number of years ago. The varied uses include polymeric monomers or intermediates for monomers as well as solvents, chemicals and drug products such as sevoflurane. However, the commercial availability of HFA is limited to only trivial amounts.
There are several reactions available which allow one to prepare HFA. Bigelow first described the direct reaction of acetone with elemental fluorine. The efforts of others to control the extreme reactivity of this reaction were partially successful, but the cost of elemental fluorine is too high to be economically viable.
The halogen exchange reaction of hexachloroacetone with hydrogen fluoride [HF] has been described in French Pat. 1,372,549, with other variations following. The reaction is performed in the vapor phase over a suitable catalyst. The preferred catalyst consists of a trivalent chromium compound. This reaction suffers from the high boiling point of hexachloroacetone which makes it hard to vaporize at industrially preferred pressures of 100 to 250 psig. Also conversion is not complete and toxic chlorofluoroacetone by-products are produced. Great care must be taken to remove these completely from the product. Finally, the product is isolated as a fluorohydrin, a compound formed from the ketone and hydrogen fluoride rather than in the ketone itself. The HFA fluorohydrin is an adduct which is sufficiently stable so that it can be distilled without decomposition. Hydrogen fluoride can be removed by supercritical distillation process. Alternatively, hydrogen fluoride can be removed by scrubbing with sodium fluoride, sulfur trioxide or NaBO
2
. All of these steps make the fluorohydrin undesirable as an intermediate in the ketone manufacture.
Suitable fluoro-olefins can be oxidized to yield HFA. U.S. Pat. No. 2,617,836 teaches the use of perfluoroisobutylene, a by-product from the production of hexafluoropropylene. However, perfluoroisobutylene's extreme toxicity precludes its shipment and handling. The oxidation of hexafluoropropylene is taught by Carlson in U.S. Pat. No. 3,536,733 to yield interalia HFA. The similar boiling points of the product, unreacted starting material and by-products which include hexafluoropropylene oxide and pentafluoropropionyl fluoride make separation tedious.
Once purified, hexafluoropropylene oxide can be isomerized to HFA, as in U.S. Pat. No. 3,213,134 with a catalyst of antimony pentafluoride. The added separations and isomerization make this preparation less convenient.
Oxidation of hexafluorothioacetone dimer is illustrated by Middleton as a convenient preparation of HFA, but the dithiane must first be prepared from hexafluoropropylene and thus adds another step to the process and additional waste in the form of sulfite/sulfate.
Direct oxidation of highly fluorinated hydrocarbons with oxygen and chlorine as initiator has been described by Haszeldine. The products are straight chain acyl halides or acids of the corresponding fluorinated hydrocarbon. Ketones were not obtained as products. A suitable hydrofluoropropane for direct oxidation to HFA would be 1,1,1,3,3,3-hexafluoropropane, R236fa. High temperature reactions of R236fa in the range of 550-585° C. have been previously described by McBee. However, the paucity of reported detail masks the fact that poor conversions are a result of poor reactivity. Thus, a highly reactive initiator such as elemental fluorine is required to oxidize R236fa directly to HFA, as illustrated in U.S. Pat. No. 5,629,460.
A disadvantage of the above fluorine initiated direct oxidation is that water is produced as a by-product. Water combines with HFA to form a hydrate, sesquihydrate and trihydrate, depending on the amount of water present. These hydrates are stable and may be sublimed or distilled without liberation of anhydrous HFA. Water must be removed from these hydrates by use of a water sequestering agent such as P
2
O
5
or SO
3
.
Thus, what is needed is a means to prepare HFA on an industrial scale from materials that are readily available, of low toxicity and easily handled. The reaction should give high conversion and yield in one step and be largely free of by-products that produce stable adducts or make separation difficult.
SUMMARY OF THE INVENTION
The foregoing objects were achieved with the present invention, which relates in general to a process for the preparation of hexafluoroacetone which comprises the reaction of 2-chloro-1,1,1,3,3,3-hexafluoropropane [R226da] with oxygen in the presence of actinic light.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a means to produce HFA in high conversions and yields by the reaction of 2-chloro-1,1,1,3,3,3-hexafluoropropane [R226da] with oxygen. The reaction can be initiated by actinic light and can be conducted in either the liquid phase or the vapor phase, in a continuous manner or as a batch reaction. Reagents which accelerate the reaction such as chlorine or fluorine etc. may be added, but that is not necessary in the presence of light.
Temperature and pressure are not critical, so the invention may be practiced at any practical temperature or pressure. Temperatures may be between about 75 and 200° C. but the preferred zone is about 85 to 150° C. The pressure may vary from subatmospheric to 500 psig; the preferred range is about 100 to 250 psig; most preferably from about 125 to 200 psig.
R226da can be made from either the hydrogenation of 2,2-dichlorohexafluoropropane or from the reaction of HF and a variety of hydrochloropropanes or chloropropenes. These reactions are outlined in part in U.S. Pat. No. 5,902,911 and PCT International Application WO 99/40053 respectively.
Another aspect of the invention is that the reaction is conducted in the presence of actinic light. Wavelengths in the ultraviolet region are especially effective and the preferred illumination is from a mercury arc lamp, which provides light of 254 nm wavelength. The outcome of the reaction is remarkable in that HFA is photochemically unstable at these wavelengths, yielding inter alia hexafluoroethane. It is not possible to presuppose that although the reaction of R226da with oxygen produces HFA that this product could be isolated in good yield. It was possible that the HFA thus formed might have decomposed at a faster rate and that most or all of the reaction products would have resulted from decomposition. In the present invention this is not the case.
The reaction of R226da with oxygen progresses in the presence of actinic light without the need of added initiators or catalysts. Alternatively, the rate of reaction may be increased by the addition of selected compounds, which act as catalysts or accelerators. Examples are chlorine, fluorine or other species capable of hydrogen atom abstraction. Under the reaction conditions atomic chlorine is photochemically generated and so this accelerator is made in situ. The use of other catalytic compounds may be affected by their continuous addition during the reaction to increase the rate.
Products of the reaction and any unconverted starting material may be isolated by any suitable means, but distillation is preferred. An advantage of the present invention over U.S. Pat. No. 5,629,460 which uses R236fa is that the by-product is principally HCl, not water or HF. HCl is the preferable by-product as HFA and HCl do not form a thermally stable adduct and mixtures of the two may be readily distilled from one another. By comparison, HFA cannot be distilled from hydrated mixtures without the benefit of a water sequestering agent such as SO
3
, P
2
O
5
or MgSO
4
. Distillation from mixtures of HF requires sodium fluoride scrubber beds or supercritical distillation techniques.
An
Halocarbon Products Corporation
Norris & McLaughlin & Marcus
Wong Edna
LandOfFree
Method for the preparation of hexafluoroacetone does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the preparation of hexafluoroacetone, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the preparation of hexafluoroacetone will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2441373