Most of the syntheses for condensation monomers using chloral employ well-known reactions between chloral and aromatic hydrocarbons, alkylaromatic hydrocarbons or substituted aromatic hydrocarbons [1, 2]. These are then followed by subsequent transformations of the diaryltrichloroethanes thus obtained.
Chloral condensations with aromatic hydrocarbons (and related derivatives) give rise to diaryltrichloroethane compounds, and are brought about in the presence of acid catalysts, proceeding with the formation of carbinol intermediates (Scheme 2.1). Commonly used catalysts include concentrated H 2SO 4 and its monohydrate, HCI, HF, P 2O 5, Lewis acids and a series of other acid agents [1, 2].
Of numerous chloral condensations with aromatic hydrocarbons the most interesting for the synthesis of condensation monomers are the reactions with benzene [3], toluene [4], acenaphthene [5], phenol [6], anisol [7], acetanilide [8] and halobenzenes like chlorobenzene [9] and fluorobenzene [10]. In general terms, these reactions proceed according to Scheme 2.2 and give the desired 1,1,1-trichloro-2,2-diarylethanes in high yields. Substituted benzenes show different reactivities which are primarily determined by orientation effects of the substituents [11].
Subsequent transformations of the 1,1,1-trichlorodiarylethanes into desired systems include:
transformation of the central 1,1,1-trichloroethane group,
hydrogen substitution in the aromatic nuclei of the diaryltrichloroethane moiety, and
transformation of functional groups introduced into the aromatic nuclei of the diaryltrichloroethane portion of the molecule.
The central trichloroethane group may be transformed into 1,1-dichloroethylene and carbonyl groups:
Of the numerous reactions the most thoroughly studied is dehydrochlorination [12] (Scheme 2.3). Common dehydrochlorinating agents include...
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