Process for preparation of aromatic compounds

Details Process for preparation of aromatic compounds Process for preparation of aromatic compounds

1999-09-13

2001-08-14

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S309000

Reexamination Certificate

active

06274770

ABSTRACT:

This invention relates to the preparation of aromatic compounds and particularly, although not exclusively, relates to the preparation of substituted benzophenone compounds, for example, 4,4′-difluorobenzophenone. 4,4′-difluorobenzophenone is an important monomeric reagent used in the production of polyketones, notably polyetheretherketone (PEEK), for example as described in EP 001 879 (Imperial Chemical Industries).
Numerous processes have been proposed for the preparation of 4,4′-difluorobenzophenone. Many known processes use fluorobenzene as a starting material. For example, JP 8961870 (Ihara) and EP 307320 (Raychem) disclose reactions which involve Friedel Crafts acylation of fluorobenzene using 4-fluorobenzoyl chloride in the presence of a catalyst. FR 2647108 (Rhone-Poulenc) discloses acylation of fluorobenzene using benzoic acid in the presence of a catalyst. Two other processes which use fluorobenzene as a starting material are described in JP 61221146 (Asahi) and EP 402623 (Rhone-Poulenc). The former process involves the reaction of fluorobenzene with carbon monoxide in the presence of oxygen and the latter process involves the reaction of fluorobenzene with phosgene to produce the desired product. One problem associated with the use of fluorobenzene is its cost. In addition, the handling and disposal of large amounts of spent catalyst used in the various processes is costly. Furthermore, some of the processes described produce relatively low yields of 4,4′-difluorobenzophenone.
Another known process is described in EP 0 004 710 (Imperial Chemical Industries) and this involves the reaction of 4,4′-diaminodiphenylmethane with an aqueous solution of sodium nitrite and hydrogen fluoride to produce 4,4′-difluorodiphenylmethane which may then be oxidised using nitric acid to produce 4,4′-difluorobenzophenone. Problems associated with this process include the corrosiveness of hydrogen fluoride and undesirable nitrogen oxide biproducts of the reaction.
Other known processes involve the oxidation of 4,4′-difluorodiphenylmethane in the presence of a catalyst, for example a cerium (IV) compound as described in JP 1172845 (Asahi) or a cobalt compound as described in JP 61183245 (Ashai). One problem associated with each of these processes is the need to dispose of the catalyst.
It is an object of the present invention to address problems associated with known processes for the preparation of substituted benzophenone compounds, for example 4,4′-difluorobenzophenone.
The invention is based on the discovery that a fluorination system can be used in both the oxidation and functionalisation of diphenylmethane derivatives for preparing substituted benzophenone compounds.
According to the invention, there is provided a process for the preparation of a compound of general formula
wherein Y and Z each independently represent a fluorine atom or a hydroxy group, and a, b, c and d independently represent 0, 1, 2 or 3 provided that the sum of a, b, c and d is 1, 2, 3 or 4, the process comprising treating a compound of general formula
wherein a, b, c and d are as described above and L
1
and L
2
each independently represent an active group provided that either Y and L
1
are different or Z and L
2
are different, with a fluorinating system in the presence of oxygen.
Unless otherwise stated in this specification, an alkyl group may have up to 10, suitably up to 8, preferably up to 6, more preferably up to 4, carbon atoms, with methyl and ethyl groups being especially preferred. Additionally, unless otherwise stated, an aryl group may be a benzyl or phenyl group, with a phenyl group being especially preferred.
Said active group is suitably a group which is not inert and can, therefore, be involved in a subsequent reaction, for example as a bridging group or a leaving group. L
1
and L
2
may be independently selected from halogen atoms, especially fluorine, chlorine and. bromine atoms, or nitro, amino, alkoxy or hydroxy groups. Said fluorinating system is preferably involved in the subsequent reaction of one or each active group.
Preferably, L
1
and L
2
each independently represent a leaving group or a group which is oxidisable to a leaving group. Leaving groups L
1
and L
2
are preferably arranged to be displaced in a nucleophilic substitution reaction involving said fluorinating system. Preferably, L
1
and L
2
each independently represent a halogen, especially a chlorine atom, or a nitro or amino group. More preferably, L
1
and L
2
each independently represent a nitro group.
L
1
and L
2
may be the same or different. Preferably, L
1
and L
2
represent the same atom or group. Preferably, Y and L
1
represent different atoms or groups and Z and L
2
represent different atoms or groups.
Preferably, a, b, c and d independently represent 0, 1 or 2. More preferably, a, b, c and d independently represent 0 or 1.
Preferably, the sum of a, b, c and d is 1, 2 or 3, and is more preferably 1 or 2. Especially preferred is the case wherein the sum is 1.
Preferably, a represents 0 or 1, more preferably 1. b may represent 0, 1 or 2 and preferably represents 0 or 1, more preferably 0.
Preferably, c represents 0 or 1, more preferably 0. Preferably, d represents 0 or 1, more preferably 0.
Preferred compounds of general formuli I and II are selected from compounds wherein a=1, b=0, c=0, d=0; a=1, b=0, c=0, d=1; a=1, b=0, c=1, d=1; a=1, b=1, c=0, d=1; a=1, b=2, c=0, d=1; and a=1, b=1, c=0, d=0. Most preferably, a=1, b=0, c=0, d=0.
Preferably, said compound of general formula II represents 4,4′-diaminodiphenylmethane or 4,4′-dinitrodiphenylmethane. More preferably, said compound of general formula II represents 4,4′-dinitrodiphenylmethane.
Compounds of general formula II may be commercially available or may be prepared using standard techniques. For example, the compounds may be prepared by reacting a 4-substituted (chloromethyl)benzene derivative, for example 4-nitro(chloromethyl)benzene, with a suitable benzene derivative in a Friedel Crafts reaction.
Said fluorinating system is preferably involved in the oxidation of the or each group —CH
2
— in said compound of general formula II. For example, said fluorinating system may catalyse the oxidation reaction. Preferably, said fluorinating system acts as a base in the oxidation reaction. It is believed that the fluorinating system, for example a fluoride ion thereof, may deprotonate the or each group —CH
2
—.
Said fluorination system is preferably involved in both the oxidation of the or each group —CH
2
— and in the reaction, for example the displacement, of the group L
1
and/or group L
2
. For example, where group L
1
and/or group L
2
represent a nitro group, said fluorinating system is preferably capable of fluorodenitrating each nitro group.
Preferably, the oxidation of the or each group —CH
2
— and the reaction of group L
1
and/or group L
2
occur in the same reaction mixture and/or in the same vessel suitably without the need for the product of one step to be isolated or otherwise separated from the reaction mixture prior to a second step. It is believed that the first step comprises the oxidation of the or each group —CH
2
— and the second step comprises reaction of group L
1
and/or group L
2
.
Said fluorinating system may include an organics soluble fluoride source and compounds for the preparation of the aforesaid in situ; and alkali metal fluorides, suitably in conjunction with a catalyst. Preferably, said fluorinating system includes one or more compounds selected from only one class of reagents, wherein one class comprises an organics soluble fluoride source as described herein and another class comprises alkali metal fluorides as described herein. The fluorinating system preferably includes only one compound from one class of reagents described herein.
Preferably, said orga

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