Trityl chloride , reaction with primary alcohols

The most widely recognized method of selective etherification of sugars and polysaccharides involves the reaction of primary alcohol groups with triphenylmethyl (trityl) chloride. Helferich60 has described the selective character of this reagent, whose rate of reaction with primary hydroxyl groups is many fold that with secondary groups. 

For example, the bulky trityl chloride selectively reacts with primary alcohol groups (see section 4.3b). The secondary alcohol groups can then be protected by acetylation or benzoylation, and the trityl group selectively removed by mild acid hydrolysis (see reaction 4.16). The reaction of tosyl chloride has also been used to selectively derivatize the primary alcohols [6]. The tosyl group can then be displaced by various nucleophiles such as halides or azide (reaction 4.14). 

The bulky triphenylmethyl or trityl (Tr) group is often employed for the regioselective protection of a primary sugar alcohol. It is conveniently introduced into partially protected sugar derivatives by treatment with trityl chloride (TrCl) in pyridine (Scheme 2.8).19 The protection can be slow but the addition of 4-(dimethyl)aminopyride (DMAP) or 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) can accelerate the reaction. 

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 SnI reaction. Here is the reaction. 

The classical method for the introduction of the trityl group involved the reaction of a primary alcohol (secondary alcohols react very slowly — if at all) with triphenylmethyl chloride (mp 110-112 °C) in pyridine [Scheme 4.209).3S3-394 The reaction can be slow and a more convenient procedure using DMAP9 or DBU395 to accelerate the reaction is applicable to large scale as shown in the... 

Selective protection of the primary hydroxy group in polyols by the trityl group can generally be accomplished by the reaction with trityl chloride in pyridine. TTie use of DMAP (0.04 equiv.) and EtsN (1.5 equiv.) facilitates the reaction. " Selective phenylation of one hydroxy group of diols can be carried out by the reaction with triphenylbismuth diacetate. While regioselectivity for primary-secondary vicinal diols is poor, only secondary alcoholic functions are converted to the phenyl ether in secondary-tertiary vicinal diols. Although phenylation of glycols occurs smoothly, monohy oxy alcohols are left essentially intact. ... 

An infrared method for the analysis of primary alcohols in polyglycols based on the reaction of the polyol with triphenylchloromethane is where the reagent consists of trityl chloride, with tris(dimethyl amino)phosphine oxide in quinoline as a solvent. This reagent is added to the sample, scanned from 3700 to 3100 cm to establish the total hydroxyl absorbance, and the reaction is then carried out in a glass-stoppered flask in a thermostatted bath at 75°C. At appropriate times, aliquots are removed and scanned, the absorbance being measured at 3280cm... 

The rates of reaction of triphenylmethyl chloride with several characteristic compounds are given ( 7) in Table I, which also illustrates the effect of the trityl chloride concentration. For the 8-fold excess, the primary alcoholic group of the galactose derivative reacts 226 times as rapidly as the secondary alcoholic group of the glucose derivative. However, the difference between the primary alcoholic group of the sorbose derivative and the secondary hydroxyl of the glucose derivative is only 34 times. 

The formation of triphenylmethyl (trityl) ethers from trityl chloride and primary or secondary alcohols is another reaction now found to be catalysed by DMAP. In this procedure, as with the silylation reported above, stoicheiometric triethylamine is used to regenerate the DMAP. Tritylone ethers (60) are more... 

Primary alcohol groups can also be mildly and selectively oxidized to carboxyl groups by reaction with 2,2,6,6-tetramethyl-l-piperidine oxoanunonium ion (TEMPO) in the presence of hypochlorite and bromide [129,130]. The specificity for the oxidation of primary alcohols in the presence of secondary alcohols in carbohydrates occurs because of the bulky nature of the TEMPO reagent, similar to the specificity obtained with the bulky trityl chloride. The mechanism for the oxidation of primary alcohols with TEMPO is given in reaction 4.140. 

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