Reactivity alcohols

The polyalkylene glycol polymer employs a starter that consists of a relatively reactive alcohol and a smaller amount of its potassium or sodium salt. With propylene oxide, for instance, initiation of the polymeri2ation then involves the starter in the following steps ... 

Acetonitrile is another participating solvent, which in many cases leads to the formation of an equatorially linked glycoside [125-131], It has been proposed that these reactions proceed via an a-nitrilium ion intermediate. It is not well understood why the nitrilium ion adopts an axial orientation however, spectroscopic studies support the proposed anomeric configuration [130,131], It is known that nucleophilic substitution of the a-nitrilium ion by an alcohol leads to P-glycosidic bonds and the best P-selectivities are obtained when reactive alcohols at low reaction temperatures are employed. Unfortunately, mannosides give poor anomeric selec-tivities under these conditions. 

The Koenigs-Knorr method in the presence of an insoluble silver salt proceeds mainly with inversion of configuration. Silver silicate and silver-silicate-aluminate have often been used as the heterogeneous catalyst. This procedure has been traditionally used for the synthesis of p-mannosidcs and has been recently reviewed.35 However, it only works well with very reactive halides and sufficiently reactive alcohol components. 

The formation of orthoester may be explained tiy the preferential addition of tlie ketene acetal to the most reactive alcohol function (primary hydroxyl g,roup) giving thc f non - i so 1 a t ed) acyclic orthoester whicti is attacked by the neighbouring OH-4 with subsequent elimination of methanol. The partial hydrolysis of the diacetate is assumed to proceed through protonation of the methoxyl group (7), via the dioxocarbenium ion 8 and the orthoacid 9. collapse of 9 by either [lath b or path a accor-ding to the mechanism generally proposed (see, for instance, ref. 29 and refs. cited therein) affords the compounds 5 or respectively. 

Less reactive alcohols (e.g., secondary alcohols) usually give lower yields. " However, Colombo and co-workers obtained a good yield of the disaccharide 345 using this method (Scheme 8.108). ... 

Problem 16.87 When reactive alcohols such as CH,=CHCH, "OH are esterified in acid, some H," 0 is found. Explain. ... 

Despite their obvious economical and ecological importance, few catalytic systems are available for the transformation of alcohols into aldehydes and ketones, using molecular oxygen or air as the ultimate, stoichiometric oxidant (5). Moreover, most of the currently available catalytic oxidation processes suffer from severe limitations, being usually only effective with reactive alcohols, such as benzylic and allylic ones, or requiring high pressures, temperatures, and catalyst loading. 

The oxidation of alcohols using azodicarboxylates has been previously reported (Yoneda, F. Suzuki, K. Nitta, Y. J. Org. Chem 1967,32,727—729). Control experiments were therefore performed to establish the need for copper salts in our oxidation procedure. Thus under our reaction conditions no aldehyde or ketone could be detected in the absence of the CuCl Phen catalyst even if phenanthroline was added as an activating base. Moreover, certain reactive alcohols were oxidized partially by CuCl Phen in the absence of the azo-derivative 19, though only in moderate yields. These control experiments thus clearly establish the key-role of the copper ion in these oxidations. 

The rate constants for addition of aliphatic alcohols and water to 19a decrease in the order MeOH > EtOH > H2O i-PrOH > t-BuOH in acetonitrile at 23 °C45, due to a combination of steric effects, nucleophilicity and acidity, all of which can be expected to affect the magnitudes of the individual rate constants involved in the mechanism for the reaction. The Arrhenius activation energy for addition of Z-BuOH to this silene, Ea = —1.7 0.4 kJmoP189, is closer to zero than that for MeOH addition, suggesting that the intracomplex product partitioning ratio is closer to 0.5 than is the case for the more reactive alcohol over the temperature range examined. It thus follows that the factor of ca 10 lower reactivity of t-BuOH compared to MeOH is mainly due to a reduction in the rate constant (kcj for initial complexation of the alcohol with the silene. 

PPh3 is not required in the chlorination of the more reactive alcohols, such as benzyl, propargyl and allyl alcohols1095. The reactions with triphosgene proceed primarily via the S 2 mechanism. 

Although only a few hydrocarbons have been studied it appears that most of them react with OH with a rate constant of ca. 109 M-1 s 1. Methane is about 4 times less reactive than this value, and cyclopentane and cyclohexane about 5 times more reactive. Alcohols, amines, ethers, and many esters also fall in the same range. Carboxylic acids and carbonyl compounds seems to be to a certain degree less reactive. Lower reactivity is also found for the protonated forms of amines and amino acids. Direct reaction of OH with the substituent is usually unimportant except for a few cases such as thiols, where H is easily abstracted from the SH, or nitroso com-... 

Nonactivated secondary alcohols were oxidized to the corresponding ketones with initial TOFs up to 100 mol mol h . Even less water-soluble and less reactive alcohols like 2-octanol could be oxidized with rates up to 20 mol moF h . Primary alcohols were oxidized to the corresponding acids. By adding TEMPO (2,2,6,6-tetramethylpiperdinyl-l-oxyl) the intermediate aldehyde could be trapped. As catalyst, the Pd complex of bathophenanthroline disulfonate (Structure 1) was used (bathophenanthroline is commercially available at approx. US 300/5 g). 

McGeary JE, Monti PM, Rohsenow DJ, Tidey J, Swift R, Miranda R Jr (2006) Genetic moderators of naltrexone s effects on alcohol cue reactivity. Alcohol Clin Exp Res 30 1288-1296... 

The hydrogenator previously described, which generates hydrogen automatically from NaBH has been adapted to hydrochlorination of reactive alcohols and olefins. The apparatus allows quantitative conversion into product without excessive contact with hydrochlorination agent.Phosphorous... 

Methods derived from the Koenigs-Knorr approach are useful for glycosylation reactions involving reactive alcohols, such as primary alcohols. Unfortunately,... 

The oxidation can also be carried out in toluene or, in the case of very reactive alcohols (allylic or benzylic), in chloroform or methylene chloride. Allylic alcohols can be selectively oxidized in acetone. 

Unstable tosylates. Tosylates have usually been prepared by reaction of the alcohol with tosyl chloride in pyridine. However, the method is not generally suitable for hindered alcohols or very reactive alcohols. Coates and Chen4 have reported a new method that is suitable for hindered or unstable tosylates. The alcohol is converted into the p-toluenesulfinate ester5 by reaction with p-toluene-sulfinyl chloride6 in ether containing 1 equivalent of pyridine yield 70-85%. The sulfinates are then oxidized to the sulfonates by m-chloroperbenzoic acid in methylene chloride at 0°, yield 75-88%. The tosylates of r-butyl alcohol, 2-bicyclo-... 

General procedure for preparation of alkyl iodides from (C6H50)3PCH3I 957 The appropriate alcohol (1 mole) is added cautiously to the crude iodide (1 mole) cooling is necessary for reactive alcohols. The method of working up is suited to the properties of the alkyl iodide ... 

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