Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2000-04-17
2001-11-06
Solola, T. A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S425000, C562S474000, C562S861000, C570S185000, C570S203000
Reexamination Certificate
active
06313337
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of making a mixture of a benzoyl halide and a benzal halide by reacting a benzotrihalide with a benzaldehyde. In particular, it relates to the use of a salt of zinc or copper, such as zinc acetate, to catalyze that reaction.
Typically, water is used to partially hydrolyze benzotrihalides and produce the corresponding benzoyl halide. Due in part to the reactivity of the product with water and the co-production of 2 equivalents of HCl, this process presents a number of processing difficulties, such as overhydrolysis, which results in the formation of the corresponding benzoic acid and the reaction of the benzoic acid with the product benzoyl halide to produce benzoic anhydride. Because the benzoic acid and anhydride have a low solubility, solids can form in the reaction mixture. The HCl generated reduces the efficiency of the still during the distillation of the product. Water and benzoyl halide can be carried into the reactor vent with the HCl by entrainment and can cause plugging by forming a benzoic acid.
These processing issues can be mitigated by reacting the benzotrihalide with a benzaldehyde rather than with water. That reaction can proceed in reasonably high yield when a strong Lewis acid, such as ferric chloride, is used. However, significant tar formation has been reported. The higher distillation temperatures required to isolate the product further increases tar formation and often significantly reduces any benefits gained over the water hydrolysis method. See “Oxygen-Chlorine Carbenoid Exchange Reaction Between Aromatic Aldehydes and Compounds Containing a Dichloromethyl Group,” by B. F. Filimonov et al. in Zh. Obshch. Khim. (1980), 50(6), 1366-72 (zinc chloride was tried as a catalyst in the reaction of benzaldehyde with o-chloro benzal chloride, but the yield was low.); “Oxygen-Chlorine Carbenoid Exchange Between Aldehydes and Compounds Containing a Trichloromethyl Group,” by B. F. Filimonov et al. in Zh. Obshch. Khim. (1979), 49(5), 1098-105; “Chlorination of Aromatic Aldehydes by Benzotrichloride in the Presence of Iron(III) Chloride,” by B. F. Filimonov et al., Zh. Obshch. Khim. (1977), 47(7), 1670; “Kinetics and Mechanism of the Chlorination of Aromatic Aldehydes with Benzotrichloride,” by G. F. Dvorko et al., Zh. Obshch. Khim. (1985), 55(8), 1828-35; and “Catalysis by Acids and Their Anhydrides of Oxygen-Chlorine Exchange Reactions Between Aryldichloromethanes and Aromatic Aldehydes,” by G. F. Dvorko et al., Zh. Obshch, Khim. (1981), 51(9), 2067-75.
In addition, benzonitriles can be made by reacting a benzotrihalide with an ammonium halide in the presence of a catalytic amount of a benzoic acid. An intermediate amide is formed, which is dehydrated by the benzotrihalide to form the nitrile and a benzoyl halide. The benzoyl halide reacts with additional ammonium halide to form additional amide and continue the cycle (see U.S. Pat. No. 5,866,709). To avoid introducing other compounds into the product mixture, the benzoic acid selected as the catalyst should correspond to the isomer of the benzotrihalide being reacted. Unfortunately, the corresponding benzoic acid catalyst is often difficult to obtain and/or is expensive. Additionally, benzoic acids have high melting points and present solids handling problems in the production of nitriles.
SUMMARY OF THE INVENTION
We have found that the reaction of benzotrihalides with benzaldehydes will proceed with a high yield of benzoyl halide when a salt of zinc or copper, such as zinc acetate, is used as a catalyst. Unlike the water hydrolysis process, stoichiometric amounts of hydrogen halide are not formed in this reaction and further hydrolysis of the benzoyl halide to form a benzoic acid is avoided. The high yielding process of this invention overcomes the process difficulties associated with water hydrolysis while also avoiding the tar-forming tendencies of strong Lewis acids. This invention can be applied to the reactions of a wide variety of aldehydes and benzotrihalides to generate the desired benzoyl chloride. The aldehyde and the amount of aldehyde used can be chosen so that the coproducts formed are easily separated.
We have also found that a nitrile can be made using a benzoyl chloride catalyst instead of a benzoic acid catalyst. The benzoyl chloride can either be produced in situ by reacting an aldehyde with the desired benzotrihalide or it can be produced as a separate product, which can then be fed as a reagent into a benzotrihalide/ammonium halide mixture. The benzaldehyde used in this reaction can be chosen based on the ease of separating the corresponding benzal chloride from the nitrile by distillation and does not need to have the same side chain substitution as the benzotrichloride. The benzaldehyde is also more reactive than the corresponding benzoic acid and forms less hydrogen halide byproduct.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In this invention, a benzotrihalide is reacted with a benzaldehyde to produce a mixture of a benzoyl halide and a benzal halide:
where each A is independently selected from halogen, CF
3
, R, or OR, each B is independently selected from halogen, CF
3
, or R, R is alkyl from C
1
to C
10
or aryl from C
6
to C
12
, each X is independently selected from Cl and Br, m is 0 to 3, and n is 0 to 2. Preferably, A is Cl or CF
3
, B is Cl, R is alkyl from C
1
to C
4
, X is Cl, m is 0 to 2, and n is 0 to 1 as those compounds are of greater commercial interest. Examples of benzotrihalides that can be used include benzotrichloride (BTC), p-chlorobenzotrichloride (PCBTC), p-bromobenzotrichloride (PBBTC), 2,4-dichlorobenzotrichloride (2,4-DCBTC), 3,4-dichlorobenzotrichloride (3,4-DCBTC), and m-trifluoromethylbenzotrichloride (MTFMBTC). Examples of benzaldehydes that can be used include benzaldehyde (BAL), o-chlorobenzaldehyde (OCBAL), p-chlorobenzaldehyde (PCBAL), and p-bromobenzaldehyde (PBBAL).
While the benzotrihalide and the benzaldehyde react equimolarly, it is preferable to use a slight excess of whichever one has a boiling point that differs the most from the boiling points of the two products (typically, this is the benzotrihalide). In this way, the reactant that has the boiling point that is closest to the boiling point of one of the products can be completely reacted and it is not necessary to separate it from the product mixture. An excess of about 2 to about 40 wt % (based on total weight of the reactants) is preferred. The following table gives some examples of options that can be used to select easily-separated products:
Boiling Point of Isomer (° C.)
Benzo-
Benz-
Benzoyl-
Benzal-
Substitution
trichloride
aldehyde
chloride
chloride
none
219-223
178-179
198
205
p-chloro
254
217
228
239
o-chloro
264
213-214
238
227-228
2,4-dichloro
288
256
3,4-dichloro
283
257
m-trifluoromethyl
210
184
The reaction is catalyzed by a zinc or copper salt like Zn(OAc)
2
, ZnCl
2
, Cu(OAc)
2
, or CuCl
2
, where “OAc” is acetate. Strong Lewis acid catalysts, such as ferric chloride, do not work well in this reaction as they tend to decompose the reactants and the products, resulting in the formation of tar. Other catalysts, such as nickel chloride and nickel acetate, also do not work well. Zinc salts are preferred since they have been found to give rapid reactions in high yield. The catalyst can be added to the reaction mixture or it may be formed in situ. At least about 10 ppm catalyst (calculated as zinc chloride and based on the total amount of reactants) should be used because the reaction is too slow if less catalyst is used. Too much catalyst is unnecessary, but not harmful; a preferred amount of catalyst is about 50 to about 500 ppm.
The reaction begins slowly and then accelerates as the level of acid halide increases. The reaction can be accelerated initially by the addition of a small amount of an acid halide to the reaction mixture, preferably the same benzoyl halide that is the product of the reaction. When Zn(OAc)
2
is used, its conversion to ZnCl
2
and acetyl chloride by the benzotrihalide is particularly useful.
Khandare Pravin M.
Lagerwall Dean R.
Lechner Mark F.
Thielen Daniel R.
Brookes Anne E.
Fuerle Richard D.
Occidental Chemical Corporation
Solola T. A.
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