Benzyl alcohols reactivity

Reaction with hydrogen halides (Sec tion 4 7) The order of alcohol reactiv ity parallels the order of carbocation staiiility RjC" > R2CH > RCHj" > CHj" Benzylic alcohols react readily... 

This IS a frequently used proce dure for the preparation of alkenes The order of alcohol reactivity paral lels the order of carbocation stability R3C > R2CH > RCH2 Benzylic al cohols react readily Rearrangements are sometimes observed... 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Ethylenediamine (70,71), benzyl alcohol and acetone (72), ethylene glycol (73) and C2—C g carboxyUc acids (74) are claimed to increase the reactivity of cellulose toward acetylation. Sodium hydroxide and Hquid ammonia (71) are excellent swelling agents and have been used to activate cellulose before esterification. Ultrasonic treatment of cellulose slurries (75) reportedly swells the fibers and improves reactivity. 

Acid chloride 5 is readily available from the known benzylic alcohol 6,4e but intermediate 4 is still rather complex. It was recognized that compound 4 could conceivably be formed in one step from 2-methoxyfuran (9)10 and iodotriflate 10. The latter compound was designed with the expectation that it could be converted to benzyne 8," a highly reactive species that could be intercepted in an intermolecular Diels-Alder reaction with 2-methoxyfuran (9) to give 7. The intermediacy of 7 is expected to be brief, for it should undergo facile conversion to the aromatized isomer 4 either in situ or during workup. 

As previously described, die main intermediates generated from die initial reaction between ortho reactive sites on novolac resins and HMTA are hydroxy-benzylamines and benzoxazines.44 Triazines, diamines, and, in die presence of trace amounts of water, benzyl alcohols and ethers also form (Fig. 7.16). Similar intermediates, with the exception of benzoxazines, are also observed when para sites react with HMTA. 

This is consistent with the observed products of oxidation, i.e. benzyl alcohol, benzaldehyde and benzoic acid and with the observed oxidation of cyclohexane. Radical-cations are, however, probably formed in oxidation of napthalene and anthracene. The increase of oxidation rate with acetonitrile concentration was intepreted in terms of a more reactive complex between Co(III) and CH3CN. The production of substituted benzophenones at high CH3CN concentration indicates the participation of a second route of oxidation. 

Whittlesey, Williams and co-workers fnrther developed the catalytic indirect Wittig reaction and fonnd that the more electron-rich NHC present in complex 18 provided a more reactive catalyst [8]. Catalyst 18 was used to convert benzyl alcohol 8 and phosphoninm ylide 19 into the product 20 under slightly milder reaction conditions and in a shorter time than in previous work (Scheme 11.4). Other C-C bond-forming reactions from alcohols using a borrowing hydrogen approach have been reported, with Peris and co-workers using Ir-NHC complexes for the C-3 alkylation of indoles with alcohols [9]. 

The low yields, which are observed among styrenyl adducts, reflect a combination of the poor reactivity of the styrene at the low temperature of the reaction. For example, the combination of t-butyl Grignard with the 2,4-bis-OBoc-benzyl alcohol 15 affords the corresponding benzopyran 50 in only 50% yield even when carried out in the presence of 5-10 equivalents of the styrene (method H, Fig. 4.27).27 Yields for substituted benzopyran styrene adducts are still lower (method G, Fig. 4.27). For example, addition of methyl lithium to 2,4-bis-OBoc-benzylaldehyde 5 followed by the addition of the dienophile and magnesium bromide affords benzopyran 51 in a paltry 27% yield. Method F is entirely ineffective in these cases, because the methyl Grignard reagent competes with the enol ether and with styrene 1,4-addition of methyl supercedes cycloaddition. 

Very reactive nitrogen mustards and aziridine-containing molecules are usually too toxic for general therapeutic use, but find use in neoplastic disease. Benzodepa (182) is such an agent. Treatment of ethyl carbamate with phosphorous pentachloride leads to cyanate 180 which readily adds benzyl alcohol to produce carbamate 181. Displacement of the active... 

A polyacrylamide with a molecular mass of 1.87 x 105 was prepared by polymerising a 5% w/v aqueous solution of acrylamide monomer in the presence of 0.15% w/w benzyl alcohol and 0.025% w/w potassium persulphate for 45 minutes at 80 °C. This product was effective in preventing the bleeding of direct dyes and hydrolysed reactive dyes from dyed cotton, which was simply dipped in a 1% solution of the polyacrylamide and dried in air [450]. 

Unlike with sodium borohydride (see Section 11.01.5.2), pyrrolizin-3-one 2 reacts with lithium aluminohydride mainly as an amide. No conjugate addition occurs, and only the reductive lactam cleavage takes place to give stereoselectively the (Z)-allylie alcohol 77. Similarly, benzo-annulated pyrrolizin-3-one 17 gives the corresponding benzylic alcohol 78. The same reactivity was observed with organometallics such as methyllithium which gives exclusively the tertiary (Z)-allylic alcohol 79 (Scheme 7). 

Fife and Benjamin, 1973. The reference reaction is attack by alkoxide on ethyl benzoate estimated from the known second order rate constant for attack by hydroxide in water at 25° (Bender, 1951) and allowing a factor of 10 for the higher reactivity of alkoxides (Gilchrist and Jencks, 1960). The pX,-value is taken as that of benzyl alcohol (Takahashi el al., 1971)... 

Certain classes of compounds are too reactive for the present method. Ethyl mandelate produced a racemic, protected phenyl glycine derivative. Benzylic alcohols with two methoxy groups (directly conjugating in the 2 and 4 positions) gave azide of 50% e.e. 

At the outset of our studies of the reactivity of I and II, it was necessary to investigate claims that tertiary henzamides were inappropriate substrates for the Birch reduction. It had been reported that reduction of A,A-dimethylbenzamide with sodium in NH3 in the presence of tert-butyl alcohol gave benzaldehyde and a benzaldehyde-ammonia adduct. We formd that the competition between reduction of the amide group and the aromatic ring was strongly dependent on reaction variables, such as the alkali metal (type and quantity), the availability of a proton source more acidic than NH3, and reaction temperature. Reduction with potassium in NH3-THF solution at —78 °C in the presence of 1 equiv. of tert-butyl alcohol gave the cyclohexa-1,4-diene 2 in 92% isolated yield (Scheme 3). At the other extreme, reduction with lithium in NH3-THF at —33 °C in the absence of tert-butyl alcohol gave benzaldehyde and benzyl alcohol as major reaction products. ... 

The reactivities of [Ru "(0)(14-TMC)(X)]"+ and its related 15-TMC, 16-TMC, and CRMes coi lexes with organic substrates have also been examined. " " In contrast to polypyridyl Ru =0 species, these macrocyclic Ru =0 complexes are weak oxidants. They oxidize benzyl alcohol to benzaldehyde but do not react with alkenes at room temperature. The lower oxidizing ability of these systems than the polypyridyl systems is due to their lower values. However, [Ru (0)(H20)(N202)](C104)2, which has a higher H value, is able to catalyze the oxidation of norbornylene, styrene, and cyclooctene by PhlO. " ... 

There are very few osmium(IV) 0x0 species. There is evidence that the Os =0 species is more reactive than the corresponding Os (0)2 species. [Os (0)2(phenba)] (see Figure 12 for structure of ligand) is able to oxidize benzyl alcohol in the presence of one equivalent of PPhs, the active... 

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