Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic halides
Reexamination Certificate
1998-12-23
2003-08-12
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic halides
C562S856000, C562S840000, C562S866000, C562S861000
Reexamination Certificate
active
06605743
ABSTRACT:
The invention relates to a continuous process for the preparation of pivaloyl chloride and of aroyl chloride, in particular of benzoyl chloride.
Pivaloyl chloride is an important synthetic intermediate in the chemical industry. It is very widely used in the synthesis of various pharmaceutical products (antiviral agents, anti-inflammatory agents) or plant-protection products (herbicides, insecticides). It is also used in the synthesis of peresters, such as tert-butyl perpivalate and tert-amyl perpivalate, which are used in particular as initiators in radical polymerization. Aroyl chlorides are also important synthetic intermediates, used in particular in the manufacture of peroxides and peresters and in the synthesis of various colorants, insecticides or rubber additives.
The main access routes to pivaloyl chloride comprise processes in which conventional reagents, such as phosgene, sulphonyl chloride, phosphorus tri- or pentachlorides, thionyl chloride or oxalyl chloride, are reacted with pivalic acid or alternatively in which carbon monoxide is reacted, in the presence of a catalyst, with tert-butyl chloride.
However, all these processes represent complex technologies, on account of the reagents involved and the need to carry out expensive treatments of the products obtained and of the effluents, which rule out industrial production.
Thus, for example in the process described by Butlerow (Justus Liebigs Ann. Chem., p. 373, 1874), which consists in reacting pivalic acid with phosphorus pentachloride according to the reaction:
(CH
3
)
3
COOH+PCl
5
→(CH
3
)
3
CCOCl+POCl
3
+HCl
the POCl
3
and the pivaloyl chloride obtained have boiling temperatures which are so close (104-106° C.) that it is virtually impossible to separate them. This author also added potassium pivalate to the reaction mixture obtained, in order to convert POCl
3
to P
2
O
5
according to the reaction:
3(CH
3
)
3
CCO
2
K+2POCl
3
→3(CH
3
)
3
CCOCl+P
2
O
5
+3KCl
Other authors (Bull. Soc. Chim. Fr., p. 350-351, 1939), in the light of this process, have proposed to prepare pivaloyl chloride directly in a single stage by reaction of sodium pivalate with POCl
3
according to the reaction:
3(CH
3
)
3
CCO
2
Na+2POCl
3
→3(CH
3
)
3
CCOCl+P
2
O
5
+3NaCl
With a 25% molar excess of sodium pivalate, the molar yield of pivaloyl chloride is only 81% with respect to the POCl
3
employed, which, of course, rules out an industrial process, all the more so since the price of sodium pivalate is much higher than the price of the desired pivaloyl chloride.
The proposal has been made to use phosphorus trichloride in place of PCl
5
(J. Am. Chem. Soc., 54, p. 3438-41, 1932) according to the reaction:
PCl
3
+(CH
3
)
3
CCOOH→(CH
3
)
3
CCOCl+H
3
PO
3
+HCl
The hydrochloric acid formed is continuously removed and the pivaloyl chloride is purified by distillation after separation by settling of the phosphorous acid, which can be recovered in value. However, the molar yield of pivaloyl chloride is less than 90% with respect to the pivalic acid employed and it is very difficult to remove the final traces of phosphorous acid (reducing product), which traces rule out the use of pivaloyl chloride in certain syntheses.
One of the most frequently mentioned processes for the synthesis of pivaloyl chloride in the literature is that employing thionyl chloride according to the reaction:
(CH
3
)
3
CCOOH+SOCl
2
→(CH
3
)
3
CCOCl+SO
2
+HCl
The reaction is generally carried out in the presence of a 20% to 50% molar excess of SOCl
2
.
According to these conditions, molar yields of distilled pivaloyl chloride are obtained which are close to 90%. The addition of catalysts, such as DMF, pyridine or N-methylacetamide, makes it possible to increase the reaction kinetics and to improve the selectivity (fall in the percentage of by-products, such as the anhydride).
However, this process has the disadvantage of resulting in a pivaloyl chloride which can comprise sulphur. In addition, in the eventuality of the use of a catalyst, the catalyst is difficult to recycle.
Pivaloyl chloride can also be obtained from phosgene according to the reaction:
(CH
3
)
3
CCO
2
H+COCl
2
→(CH
3
)
3
CCOCl+HCl+CO
2
or alternatively by carbonylation of tert-butyl chloride in the presence of catalysts, such as AlCl
3
or FeCl
3
, according to the reaction:
(CH
3
)
3
CCl+CO→(CH
3
)
3
COCl
However, these processes exhibit the disadvantage of using highly toxic reagents which are difficult to handle and requiring the use of catalysts in order to obtain a good selectivity and yields of greater than 90%.
It should be noted that, in the case of the carbonylation of tert-butyl chloride, the use of catalysts is capable of resulting in the formation of impurities or of causing the retrogression of the product formed.
The access routes to aroyl chlorides, in particular to benzoyl chloride, also comprise processes in which conventional reagents, such as PCl
5
, COCl
2
or SOCl
2
, are reacted with aromatic acids.
More specifically, benzoyl chloride is obtained industrially by partial hydrolysis of phenylchloroform according to the reaction:
C
6
H
5
CCl
3
+H
2
O→C
6
H
5
COCl+2HCl
or by reaction of benzoic acid with phenylchloroform according to the reaction:
C
6
H
5
CCl
3
+C
6
H
5
CO
2
H→2C
6
H
5
COCl+HCl
The simultaneous production of pivaloyl chloride and of aroyl chloride, more specifically of benzoyl chloride, is not described to any great extent in the literature.
This simultaneous production of acid chlorides is based on the reaction:
RCOOH+C
6
H
5
CCl
3
→RCOCl+C
6
H
5
COCl+HCl
which is a chlorodehydroxylation reaction of RCOOH by C
6
H
5
CCl
3
.
Thus, in Patent JP 86-021 617 B, a process for the batchwise preparation of pivaloyl chloride and of benzoyl chloride is disclosed.
This process consists in reacting, in a first stage, pivalic acid and phenylchloroform in a stoichiometric amount at atmospheric pressure in the presence of FeCl
3
at a temperature ranging from 40° C. to 150° C. and then, after removal of the HCl formed, in distilling the pivaloyl chloride under reduced pressure. Subsequently, in a second stage, after introduction of a fresh charge of catalyst, the reaction mixture is heated to a temperature of between 40° and 160° C. and then the benzoyl chloride formed is distilled under reduced pressure.
Although this process makes it possible to obtain acceptable yields, of between 90% and 95%, of pivaloyl chloride and of benzoyl chloride, there are a number of disadvantages to this way of operating.
Thus, it is necessary to remove all the pivaloyl chloride before carrying out the second stage, at the risk of decarbonylating the pivaloyl chloride according to the reaction:
In order to avoid this, the authors of the patent mentioned completed the distillation by extracting the residual pivaloyl chloride by partial distillation under reduced pressure of the benzoyl chloride formed. Under these conditions, the distillating fraction is composed essentially of benzoyl chloride, with a few % of pivaloyl chloride and of other unidentified compounds.
There is a significant disadvantage to this way of operating, when it is known that various by-products are capable of being formed as a result of side reactions, the most important of which are the following:
an equilibrium transhalogenation reaction between benzoyl chloride and pivalic acid:
the reaction of the benzoic acid formed with benzoyl chloride, to result in benzoic anhydride:
C
6
H
5
CO
2
H+C
6
H
5
COCl→(C
6
H
5
CO)
2
O+HCl
These by-products formed during the first stage are difficult to avoid. The authors of the patent mentioned also, in the second stage, added a significant amount of FeCl
3
in order to convert the by-products and in particular benzoic anhydride in the presence of unconverted C
6
H
5
CCl
3
according to the reaction:
(C
6
H
5
CO)
2
O+C
6
H
5
CCl
3
→3C
6
H
5
COCl
Finally, this batch process exhibits lengthy,
Corbiere Philippe
Ruppin Christophe
Elf Atochem S.A.
Millen White Zelano & Branigan P.C.
Oh Taylor V.
Rotman Alan L.
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