BACKGROUND OF THE INVENTION
Acid fluorides, chlorides and bromides are a known class of compounds having known utilities. Many methods of preparing such compounds from the corresponding acids or acid salts are known, as illustrated by R. B. Wagner and H. D. Zook, "Synthetic Organic Chemistry," John Wiley & Sons, Inc., N.Y., N.Y. (1953), Chapter 17. Other methods of preparation of aromatic acid halides are illustrated by N. Rabjohn, Journal of the American Chemical Society (J.A.C.S.), 76, 5479 (1954), and by R. C. Schreyer, J.A.C.S., 80, 3483 (1958), wherein iso-and terephthalyl chloride were prepared from α, α, α, α', α', α'-hexachloro-m or p-xylene.
SUMMARY OF THE INVENTION
A novel method of preparing acid fluorides, chlorides and bromides has now been discovered which comprises reacting in the presence of a Lewis acid catalyst (a) sulfur dioxide and (b) an organic compound containing at least one allylic and/or benzylic trihalomethyl group, i.e., a trifluoromethyl, trichloromethyl or tribromomethyl group, or a mixed halomethyl group.
The novel process is illustrated by the following reaction equation: ##SPC2##
Wherein X is fluoro, chloro or bromo; LA is a Lewis acid, and R is an n-valent hydrocarbon or halo-substituted hydrocarbon radical, wherein the carbon atom of attachment is unsaturated and n is an integer from 1 to about 4, and is preferably 1 or 2.
The advantages of preparing acid halides according to the subject process are (a) high product yields of II, and (b) the production of the reaction by-products, III, thionyl halides which are themselves useful and desirable products. The thionyl halides are volatile components easily separated and recovered from the reaction mixture by common distillation techniques.
Suitable reactants in the process are a known class of compounds which is generically represented by (I) above. Examples of suitable reactants within formula I are those having (1) allylic trihalomethyl groups, such as those having the structural formula R1 R2 C=C(R3)--CX3, wherein R1, R2 and R3 are hydrogen, X, hydrocarbon groups or halo-substituted hydrocarbon groups having 1 to about 20 carbon atoms, e.g., alkyl, aryl, cycloalkyl, alkaryl, aralkyl, etc., and include for example those having the following values for X and R1 -R3 :
Table I ______________________________________ X R1 R2 R3 ______________________________________ F H H H Cl H H H Br H H H F F F F Cl Cl Cl Cl Br Br Br Br Cl CH3 H H Cl CH3 C2 H5 H Cl CCl3 H H Cl CCl3 Cl Cl F C2 H5 H H F H H C2 H5 Br n-C5 H11 H CH3 F n-C10 H21 H H Cl cyclohexyl H H Br C6 H5 H H Cl C6 H5 Cl Cl F C6 H5 C6 H5 H Cl β-naphthyl H CH3 Cl P-CH3 -C6 H4 H H F 3,5-(CH3)2 -C6 H3 3,5(-CH3 -)2 C6 H3 H Cl H H C6 H5 Br C6 H5 -C2 H4 H H Cl CH2 =CH- H H F CH2 =CH- H CH=CH2 F CF2 =CF- F F ______________________________________
and other like compounds, or (2) benzylic trihalomethyl groups, such as those in formula I wherein ##SPC3##
and other like compounds. Preferred reactants are those in formula I wherein X is chloro, and the most preferred reactants are 1,1,1-trichloropropene, perchloropropene, 1,2-bis(trichloromethyl)ethylene, perchlorobutene-2, benzotrichloride, α,α,α,α',α',α'-hexachloro-m- or p-xylene, α,α,α,α',α',α'-hexachloro-p,p'-bitolyl , α,α,α,α',α',α'-2,5-octachloro-p-xylen e, perchloro-p-xylene, perchloro-p,p'-bitolyl.
Any one or any mixture of the known class of Lewis acids may be included in the instant reaction as a catalyst. Examples of suitable such catalysts include BF3, BF3.etherate, AlCl3, AlBr3, FeCl3, FeBr3, SnCl4, ZnCl2, and other like compounds. Preferably, the halogen in the catalyst is the same as the X in the trihalomethyl group(s) attached to R. A catalytic amount of Lewis acid catalyst is required in the reaction, such as amounts up to about 10 percent by weight or more based on the weight of R CX3)n reactant. Typically, the preferred amount of catalyst is between 0.01 and 1 percent by weight, same basis.
SO2 is suitably used in substantially any amount in the reaction. However, the stoichiometry of the reaction requires one mole of SO2 per --CX3 group. Hence, at least one mole of SO2 per --CX3 group is preferred, and an excess of SO2 is most preferred. This preference is based on the fact that excess SO2 acts not only to drive the reaction to completion but also acts as a reaction solvent.
Other compounds may be advantageously used as solvents so long as they are inert in the reaction, i.e., they do not react with any of the reactants or products. Examples of such compounds include carbon tetrachloride, perchloroethylene, and other like halogenated hydrocarbons. A reaction solvent is preferred since the reaction is exothermic and the dissipation of heat is thus enhanced.
The reaction is suitably conducted at a temperature between about -20°C. and about 150°C., and a temperature between about 50°C. and 125°C. is preferred. The reaction occurs at temperatures above and below the suitable temperature range but at temperatures below about -20°C., the reaction rate is too low to be practical, and at temperatures above about 150°C., the reaction rate is high and the reaction is difficult to control unless high pressure apparatus is used.
The reaction pressure is suitably atmospheric or superatmospheric pressure, and autogenous pressure is presently preferred. Pressures of 1 atm. to 40 atm. are typical at temperatures of 25°C. to 120°C.
The reaction is preferably conducted under substantially anhydrous conditions.
The reaction time will vary in accordance to the reactivity of the R--CX3)n reactant, the catalyst used and the reaction temperature. Generally a reaction time of a few minutes to a few days is sufficient for the reaction to be substantially completed, e.g., about 1 to about 96 hours. In most instances, 4 to 24 hours at the preferred reaction temperatures is adequate for the reaction to go to substantial completion. The more highly substituted compounds, particularly those wherein the substituent is halogen or haloalkyl, react faster than the corresponding unsubstituted compounds.
The reactivity of a catalyst is determined by its relative acidity as a Lewis acid, as illustrated by D. P. N. Satchell et al., Chemical Reviews, Volume 69, No. 3, page 251 (1969). The more acidic Lewis acids, such as BF3 and AlCl3, cause faster reaction than the weaker Lewis acids, such as SnCl4 and ZnCl2.
The order of addition is not critical and the reaction may be conducted as a batch process or a continuous process wherein the reactants are charged continuously or incrementally.
The following examples further illustrate the invention.
GENERAL EXPERIMENTAL PROCEDURE
A catalytic amount of Lewis acid catalyst was added to 0.1 mole of trihalomethyl-containing reactant. The mixture was cooled in liquid nitrogen and 0.2 mole of liquid SO2 was added. The reaction vessel was sealed, warmed to reaction temperature and held at that temperature until the reaction was substantially completed, cooled to room temperature and opened to the atmosphere. The volatile components were removed under reduced pressure, and the acid halide product obtained from the reaction mixture by distillation under reduced pressure or by solvent extraction with an appropriate solvent.
Preparation of Trichloroacryloyl Chloride ##SPC4##
In accordance with the above general procedure, 0.5 g. (0.0038 mole) of anhydrous AlCl3 was mixed with 24.9 g. (0.1 mole) of perchloropropene and 12.8 g. (0.2 mole) of SO2. The reaction mixture was warmed at 90°C. for 39 hours in a sealed, glass polymer tube. Upon distillation, 13.3 g. of trichloroacryloyl chloride (69% yield, based on perchloropropene) and 8.2 g. of thionyl chloride (69% yield) were obtained.
Preparation of Benzoyl Chloride ##SPC5##
In accordance with the above general procedure, 5.0 g. (0.037 mole) of anhydrous ZnCl2 was mixed with 7.82 g. (0.04 mole) of benzotrichloride and 5.0 g. (0.08 mole) of SO2. The reaction mixture was warmed at 120°C. for 48 hours in a sealed glass polymer tube. Upon distillation, 3.23 g. of benzoyl chloride (58% yield, based on benzotrichloride) was obtained.
Two other identical reactions were conducted as above except that in one reaction AlCl3 was used rather than ZnCl2, and FeCl3 replaced ZnCl2 in the other reaction. The best product yield was obtained in the AlCl3 catalyzed reaction.
Under similar reaction conditions and ratio of reactants, several reactions were conducted in the presence of a catalytic amount of AlCl3. The results are summarized in Table III.