Triphenylmethyl group

Additional phenyl substituents stabilize carbocations even more Triphenylmethyl The triphenylmethyl group is 1, , t 11 1. . 1. .. 

BAEYER VILLIGER Tritylalion Introduction of a triphenylmethyl group into an aromatic ring... 

The monothioacetal is also stable to 12 N hydrochloric acid in acetone (used to remove an TV-triphenylmethyl group) and to hydrazine hydrate in refluxing ethanol (used to cleave an A -phthaloyl group). It is cleaved by boron trifluoride etherate in acetic acid, silver nitrate in ethanol, and tiifluoroacetic acid. The monothioacetal is oxidized to a disulfide by thiocyanogen, (SCN)2- ... 

The bulky triphenylmethyl group has been used to protect a variety of amines such as amino acids, penicillins, and cephalosporins. Esters of N-trityl a-amino acids are shielded from hydrolysis and require forcing conditions for cleavage. The a-proton s also shielded from deprotonation, which means that esters elsewhere in the molecule can be selectively deprotonated. 

The optically active poly(TrMA) shows a large optical activity and intense circular dichroism (CD) due both to the triphenylmethyl group, indicating that this group has a chiral propeller structure, and to the helicity. Poly(TrMA) of degree of polymerization (DP) over 80 is insoluble in common organic solvents. 

A protector of unique nature is the triphenylmethyl group, which is benzyl sensitized by two phenyl groups on the exocyclic carbon atom. When affixed to a hetero atom, the bond is cleavable by mild acid or hot acetic acid in part because of the very stable cation that is formed (Figure 3.25). Af -Triphenylmethylamino... 

FIGURE 3.25 The triphenylmethyl group for protection63-64 of side-chain and carboxy-ter-minal functional groups. The triphenylmethyl-heteroatom bond is sensitive to mild acid. 

Table VII the electron-beam exposure characteristics are given for the soluble poly (triphenylmethyl methacrylate-co-methyl methacrylate)s. The sensitivity on alkaline development was strongly influenced by the copolymer composition. The highest sensitivity was obtained on the copolymer containing 93.7 mol% methyl methacrylate. The copolymer of highest sensitivity showed the 7-value of 6.3, which was nearly twice as large as that for poly(methyl methacrylate). Formation of methacrylic acid units on exposure is obvious from the infrared spectrum. However, the mechanism of the occurrence should be different from the case of the a,a-dimethylbenzyl methacrylate polymer since there are no /3-hydrogen atoms in the triphenylmethyl group, and may be similar to the case of poly (methyl methacrylate). This will be explored in the near future.

The triphenylmethyl group is often referred to as a trityl group. 

The triphenylmethyl group can be removed from the amine nitrogen under very mild conditions, either by catalytic hydrogenation or by hydrolysis in the presence of a weak acid ... 

The distances within the SiN2Al unit for the compounds 66,67,72, and 73 vary in the range 1.70-1.79 A for Si-N and 1.85-1.97 A for Al-N. The aluminum-carbon distances are in the range 1.97-2.06 A. The magnesium carbon distance in 72 is quite elongated [2.20(1) A], a feature that might be related to some extent to the triphenylmethyl group. 

Thus, an intermediate similar to ammonium salt 135 would be formed first and it would then undergo a syn-elimination by the loss of Hg to give only iminium ion 133 since the triphenylmethyl group and the methine hydrogen in 135 lie on opposite faces of the molecule. 

The bulky triphenylmethyl group can be introduced also at the sterically hindered axial position of 1,6-anhydro sugars. With 3 molar equiv. of the reagent at 85-90 °C for 24 h, more than 8% of 2-acetamido-l,6-anhydro-2-deoxy-3-0-trityl-P-D-gluco-pyranose (45) has been obtained [317] from (43). The 4-trityl ether [i.e., (44)] was, of course, the major product, just as in the case of tritylation of l,6-anhydro-2-0-p-toluenesulfonyl-P-D-glucopyranose [318] or, l,6-anhydro-2-0-benzyl-P-D-glucopyra-nose [229]. 

However, it was not possible to obtain l-trityl-2-nitroimidazole by this method as, for example, also during the nitration of the lithium derivative of 1-tritylimida-zole by nitronium tetrafluoroborate [356], This is probably due to the elimination of the triphenylmethyl group during nitration. However, it was possible to obtain l-trityl-2-nitroimidazole by using propyl nitrate as nitrating agent [356], The product... 

The compound has a similar appearance and the same properties as the sodium deri ative. It exhibits, however, this difference, that whilst sodium triphenyl is unstable in the presence of ammonia, the potassium compound is stable even at 100° C. Moreover, it has not been found possible to synthesise the triphenylmethyl group by the action of triphenylmethyl chloride on potassium triphenylmethyl. 

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