Triphenylmethyl s. a. Trityl

Tritio compounds s. Compounds, H-labeled, Ditritio compds. Triton B 26, 270 27, 456, 917 Trityl... s. a. Triphenylmethyl... N-Tritylacoxylamines... 

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. 

If (A i[X ]/A 2[Y ]) is not much smaller than unity, then as the substitution reaction proceeds, the increase in [X ] will increase the denominator of Eq. (8-65), slowing the reaction and causing deviation from simple first-order kinetics. This mass-law or common-ion effect is characteristic of an S l process, although, as already seen, it is not a necessary condition. The common-ion effect (also called external return) occurs only with the common ion and must be distinguished from a general kinetic salt effect, which will operate with any ion. An example is provided by the hydrolysis of triphenylmethyl chloride (trityl chloride) the addition of 0.01 M NaCl decreased the rate by fourfold. The solvolysis rate of diphenylmethyl chloride in 80% aqueous acetone was decreased by LiCl but increased by LiBr. ° The 5 2 mechanism will also yield first-order kinetics in a solvolysis reaction, but it should not be susceptible to a common-ion rate inhibition. 

An exceptionally stable cation is formed when three benzene rings can help to stabilize the same positive charge. The result is the triphenylmethyl cation or, for short, the trityl cation. The symbol Tr (another of these organic elements ) refers to the group Ph3C. Trityl chloride is used to form an ether with a primary alcohol group by an S l reaction. Here is the reaction. 

Now we can strip away the protecting groups one by one and it is instructive to see how selective these methods are. The trityl group comes off in aqueous acetic acid by another S l reaction in which water captures the triphenylmethyl cation, and the benzyl group is removed by hydrogenoly-sis—hydrogen gas over a 10% palladium on charcoal catalyst in ethanol. 

Many groups are available for the protection of the nitrogen unit of an amino acid. Sulfonyl chlorides are commonly used an example is the reaction of isoleucine with p-toluenesulfonyl chloride under basic conditions to give the A -sulfonyl derivative. Another N protecting group is a tertiary halide called triphenylmethyl chloride (PhgCCl called trityl chloride). When it reacts with valine (55) under basic conditions, the product is the W-trityl amino acid 143. The mechanism of this reaction is probably a modified S l, but it will not be discussed here. ... 

Ethyl nitrite poured on trityl mercaptan (under a Ng-atmosphere, which is kept up throughout the entire operation) at 15°, gently shaken, excess ethyl nitrite allowed to evaporate at room temp., and the resulting ethanol removed in vacuo crude triphenylmethyl thionitrite. Y ca. 100%. F. e. with low yield, also thionitrates, s. G. Kresze and U. Uhlich, B. 92, 1048 (1959). 2-Thia- l,3-diazaadamantanes O... 

More than forty years ago it was shown that triphenylmethyl (trityl) acetate solvolyzes in either aqueous dioxane or methanol almost entirely by alkyl-oxygen bond fission. In addition, a general tendency has been observed towards faster solvolyses of this type in solvents of higher ionizing power, consistent with a dissociative (S l) mechanism, with a carboxylate leaving group. 

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