Trityl chloride, reactions

The addition of chloride ion to the medium in the case of the trityl chloride reaction reduces the net rate by virtue of the back reaction to regenerate trityl chloride. The product composition in the presence of various added reagents is a quantitative measure of the relative reactivity of the added reagents towards the carbonium ion. The results are summarized in Table VI. 

StericaHy hindered silyl ethers such as ferZ-hutyl dimethyl silyl, / fZ-butyldiphenylsilyl, and tricyclohexylsilyl have been proposed as alternatives to trityl ethers. Reaction of sucrose with 3.5 molar equivalents of ferZ-hutyl dimethyl silyl chloride produces the 6,1/6 -tri-O-silyl derivative in good yield (27). 

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. 

If the alkyl halide contains more than one, equally reactive C-halogen centers, these will generally react each with one aromatic substrate molecule. For example dichloromethane reacts with benzene to give diphenylmethane, and chloroform will give triphenylmethane. The reaction of tetrachloromethane with benzene however stops with the formation of triphenyl chloromethane 7 (trityl chloride), because further reaction is sterically hindered ... 

In subsequent studies,22 Sheehan et al. demonstrated that the action of diisopropylcarbodiimide on penicilloate 24, prepared by protection of the free primary amino group in 23 with trityl chloride (see Scheme 6b), results in the formation of the desired -lactam 25 in a very respectable yield of 67 %. In this most successful transformation, the competing azlactonization reaction is prevented by the use of a trityl group (Ph3C) to protect the C-6 amino function. Hydrogenolysis of the benzyl ester function in 25, followed by removal of the trityl protecting group with dilute aqueous HC1, furnishes 6-aminopenicillanic acid (26), a versatile intermediate for the synthesis of natural and unnatural penicillins. 

The source of some of the difficulties encountered in trying to explain the effects of structural changes on ionization rates may be due to the different parts played by the solvent, as for example, the sulfur dioxide of the trityl chloride equilibrium experiments and the aqueous acetone of the benzhydryl chloride rate data. The solvent is bound to modify the effect of a substituent, and although the solvent is usually ignored in discussing substituent effects this is because of a scarcity of usable data and not because the importance of the solvent is not realized "... solvation energy and entropy are the most characteristic determinants of reactions in solution, and... for this class of reactions no norm exists which does not take primary account of solvation. 220 Precisely how best to take account of solvation is an unanswered problem that is the subject of much current research. 

The addition of a cation to an olefin to produce a carbonium ion or ion pair need not end there but may go through many cycles of olefin addition before the chain is eventually terminated by neutralization of the end carbonium ion. Simple addition to the double bond is essentially the same reaction stopped at the end of the first cycle. The addition of mineral acids to produce alkyl halides or sulfates, for example, may be prolonged into a polymerization reaction. However, simple addition or dimerization is the usual result with olefins and hydrogen acids. The polymerization which occurs with a-methyl-styrene and sulfuric acid or styrene and hydrochloric acid at low temperatures in polar solvents is exceptional.291 Polymerization may also be initiated by a carbonium ion formed by the dissociation of an alkyl halide as in the reaction of octyl vinyl ether with trityl chloride in ionizing solvents.292... 

The reactions of 6-indazolylaminomethylenemalonate (1470) with benzyl chloride and with trityl chloride in a mixture of DMF and ethanol and... 

Quinn et al. followed the reaction of a nucleoside with trityl chloride in pyridine at 50 °C on the laboratory scale. This reaction is the first step of an industrially significant process. The UV-vis spectra were analyzed with chemometric analysis where automatic window factor analysis (WFA) yielded better results than PLS. A reactive intermediate, a solvated carbocation, was identified that had not been found with HPLC (quenching upon aliquot dilution) or NIR, respectively. Small, sudden process upsets could be detected. 

The catalytic activity of the trityl moiety was unobjectionably adjusted in the addition reaction of the allylstannanes to aldehydes [148]. In this allylation process the trityl chloride 52, due to its disposition to partially ionic character of the halogen bonding, was employed as a catalyst in the complementary tandem with weak Lewis acid TMSCl (Scheme 57). The excess of the silyl component was necessary in order to release the trityl catalyst from the intermediate to complete the catalytic cycle. The achieved yield was 93%, when trityl chloride 52 was used. 

Alkylation of 5-amino-1,2,4-thiadiazoles (17) with methyl iodide leads to N-4 derivatives of type (18) which undergo a Dimroth rearrangement to (110) on warming in ethanol when R = H (Scheme 26). When R = methyl, phenyl, or benzyl the reaction is severly hindered <84CHEC-I(6)463>. In contrast, benzhydryl and trityl chlorides (which are harder electrophiles) alkylate (17) at the 5-amino function to give compounds of type (109) (Scheme 26). 

The synthesis of losartan potassium (1) by the process research chemists at Merck is outlined in the following (Griffiths et ak, 1999 Larsen et al., 1994). Phenyltetrazole (8) is protected as the trityl phenyltetrazole 9 (Scheme 9.3). Ortho-lithiation of 9 followed by quenching with triisopropyl borate afforded boronic acid 10 after treatment with aqueous ammonium chloride. Reaction of glycine (11) with methyl pentanimidate (12) in a methanol/water mixture yielded (pentanimidoylamino) acetic acid (13), which underwent a Vilsmeier reaction with phosphorous oxychloride in DMF followed by hydrolysis to give imidazole-4-carbaldehyde 14 in moderate yield. 

Tritylation (9. 179).3 4-Dimethylamino-N-triphenylmethylpyridinium chloride (I) has been prepared by reaction of trityl chloride with DMAP. It has been presumed to be the effective reagent in tritylations cataly7ed by DMAP. It does... 

The scope and limitations of the Lewis acid-catalyzed additions of alkyl chlorides to carbon-carbon double bonds were studied.51 Since Lewis acid systems are well-known initiators in carbocationic polymerizations of alkenes, the question arises as to what factors govern the two transformations. The prediction was that alkylation products are expected if the starting halides dissociate more rapidly than the addition products.55 In other words, addition is expected if the initial carbocation is better stabilized than the one formed from the dissociation of the addition product. This has been verified for the alkylation of a range of alkyl-and aryl-substituted alkenes and dienes with alkyl and aralkyl halides. Steric effects, however, must also be taken into account in certain cases, such as in the reactions of trityl chloride.51... 

The reaction of indazole with trityl chloride yields, together with expected 1- and 2-substituted derivatives, 3-tritylindazole (110) which is unprecedented in indazole chemistry (85BSB421). Benzyl chloride and diphenylmethyl chloride behave classically in this respect (85H(23)2895). 

Tritylamines can serve as both linkers and protective groups for aliphatic amines because, unlike benzhydrylamines, they do not usually undergo acylation when treated with activated acid derivatives. Tritylation of aliphatic amines is readily accomplished by adding excess amine to a support-bound trityl chloride. Illustrative cleavage reactions are listed in Table 3.21. 

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. 

The high regioselectivity of reactions of the salts 231 with various electrophilic agents was demonstrated by alkylation of 5-(3-chloropropyl)-l //-tctrazolc 250 with trityl chloride resin in the presence of Et3N. The corresponding resin containing the Nz-isomer 251 was obtained (Equation 39) <2000JC019>. 

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. 

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