Trichloromethyl groups

BenZotrichloride Method. The central carbon atom of the dye is supphed by the trichloromethyl group from iJ-chlorobenzotrichloride. Both symmetrical and unsymmetrical triphenyhnethane dyes suitable for acryhc fibers are prepared by this method. 4-Chlorobenzotrichloride is condensed with excess chlorobenzene in the presence of a Lewis acid such as aluminium chloride to produce the intermediate aluminium chloride complex of 4,4, 4"-trichlorotriphenylmethyl chloride (18). Stepwise nucleophihc substitution of the chlorine atoms of this intermediate is achieved by successive reactions with different arylamines to give both symmetrical (51) and unsymmetrical dyes (52), eg, N-(2-chlorophenyl)-4-[(4-chlorophenyl) [4-[(3-methylphenyl)imino]-2,5-cyclohexadien-l-yhdene]methyl]benzenaminemonohydrochloride [85356-86-1J (19) from. w-toluidine and o-chloroaniline. 

This result shows than the initially added trichloromethyl group has little influence on the stereochemistry of the subsequent bromine atom-abstraction. The intermediate 2-(trichlor-omethyl)cyclohexyl radical presumably relaxes to the equatorial conformation faster than bromine-atom abstraction occurs. In contrast with addition to A -octahydronaphthalene, the addition is exclusively /ran -diaxial ... 

The /rans-fiised decalin system is conformationally rigid, and the stereochemistry of the product indicates that the initial addition of the trichloromethyl radical is from the axial direction. This would be expected on stereoelectronic grounds, because the radical should initially interact with the n orbital. The axial trichloromethyl group then shields the adjacent radical position enough to direct the bromine abstraction in the trans sense. 

This is again the result of steric shielding by the trichloromethyl group, which causes the bromine atom to be abstracted from the endo face of the intermediate radical. 

This topic has been reviewed [2, pp 94, 100-111, 130-134] All of the standard approaches to the synthesis of a compound like methyl 2-fluorostearate from methyl 2-bromostearate result mall yield of the 2-fluoro ester and the unsaturated esters. Although silver fluoride is not a new reagent, its use moist in wet acetonitrile to convert methyl 2-bromostearate to its fluoro ester is a departure from the traditional set of anhydrous conditions (Procedure 6, p 194) [71] In contrast, silver tetrafluoroborate converts a-chloroketones to their respective fluoroketones under anhydrous conditions. The displacement of less activated halogen groups by silver tetrafluoroborate to form their respective fluorides is novel Although silver tetrafluoroborate could not be used to convert an aliphatic terminal dichloromethyl or trichloromethyl group to its corresponding fluoro derivative, it is an effective fluorine source in other situations [72] (Table 8)... 

The carbonyl carbon of perfluoro acyl halides and carboxylic acids can be converted to a trichloromethyl group [67] (equation 54)... 

The activating effect of a trichloromethyl group is seen in the 2-dechlorination reactions of 2-chloro-4,6-bis(trichloromethyl)-s-tria-zine (175) with arylsulfonylhydrazides (24 hr) and heterocyclic amines (3 hr) at 20° and with unbasifled primary and secondary alcohols (65°, 30 min). The 4,6-diphenyl or 4,6-bis(4-chlorophenyl) analogs do not react in this manner. ... 

The cycloaddition of aldehydes and ketones with ketene under the influence of quinine or quinidine produce chiral 2-oxetanones [46,47]. Solvolytic cleavage of the oxetanone, derived from chloral, and further solvolysis of the trichloromethyl group leads to (5)- and (R)-malic acids with a 98% ee [46] (the chirality of the product depends on the configuration of the catalyst at C-8 and, unlike other alkaloid-induced reactions, it is apparently independent of the presence of the hydroxyl group). No attempts have been made to catalyse the reaction with chiral ammonium salts. 

The copolymer described in Ex. 6.1 in which the trichloromethyl group is connected to the 2-position of a 1-phenylethane-1,2-diyl unit and the chlorine to the 1-position of a 1-chloroethane-l,2-diyl unit ... 

While the 5-trichloromethyl group of (65) furnishes the 5-oxo compound when treated with KOH (Equation (14)), the 3-trichloromethyl isomer (66) gives the carboxylic acid (67), which quickly rearranges to acetyl cyanamides with loss of CO2 (Scheme 23) (64HCA838>. 

Reaction of 5-trichloromethyl-1,2,4-thiadiazoles with secondary amines leads to amides. For example, treatment of (84) with piperidine gives (86) which presumably arises by nucleophilic displacement of chloride ion from the trichloromethyl group, followed by hydrolysis during work up of the resulting dichloro compound (85) (Scheme 21) <86PS(26)151>. 

The reaction of methanesulfonyl chloride CH3SO2CI (to generate in situ the reactive sulfene CH2=S02) with chloral in triethylamine produced a /8-sultone bearing a trichloromethyl group at position Sultones... 

The trimethylsilyl group is not as effective as the tert-butyl group in reducing the energy separation between benzene and Dewar benzene (60 kcal/mol according to the above analysis), while the trichloromethyl group is about as effective as (37 vLy kcal/mol). It appears that steric effects alone are not sufficient to overcome the large preference for benzene. 

Trichloromethyl oxadiazoles can be prepared by the classical reaction from trichloracetamidoxime and acid anhydrides or chlorides. The trichloromethyl group is resistant under mild hydrolysis conditions such as hydrazine, ammonia or cold alkali treatment with boiling alkali leads to the salt of 3-carboxyoxadiazoles (see p, 845) 25a, 55b). 

It was recognized in the 1930s that Swarts work on (trifluoromethyl)benzene opened the way to the synthesis of many side-chain-fluorinated arenes. Aryl trichloromethyl groups were found to be readily converted to trifluoromethyl groups by anhydrous hydrogen fluoride, and systematic work in the area was initiated. This included commercial investigations, and patents were filed on potential uses of both side chain and nuclear fluorinated arenes. 

Trichloromethyl groups linked to an ether oxygen have high reactivity towards hydrogen fluoride. Thus, complete Cl-F replacement is achieved by heating the reactants in an autoclave, e.g. reaction of 5226 (see also Houben-Weyl, Vol. E4, pp 627-628). 

Exhaustive exchange of chlorine atoms for fluorine can take place in l-(dichloromethyl)-2-(trichloromethyl)benzene treated with antimony(III) fluoride, while under the action of hydrogen fluoride the exchange occurs only in the trichloromethyl group.13... 

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