Deprotonations alcohols, sodium hydride

The alcohol has a piCa close to that of water, so hydroxide is not a good choice for complete deprotonation, and sodium hydride is commonly used for this purpose. Hydroxide will however deprotonate both the carboxylic acid, to make a carboxylate salt, or the ammonium ion, to make the free amine. Bicarbonate is also commonly used for this purpose although it is only just basic enough to do the job, the deprotonation reaches completion because it is not an equilibrium protonated bicarbonate forms carbonic acid which decomposes irreversibly to water and carbon dioxide. 

Both NaH and KH are used to deprotonate alcohols. KH is more reactive than NaH. Compare atomic charges and electrostatic potential maps of potassium hydride and sodium hydride. For which is the hydrogen more negatively charged Which should be the better source of hydride ... 

During the benzylation of an alcohol the hydroxy functionalities are turned into alkoxides. Therefore NaH is necessary. Next benzyl bromide is added. For an efficient alkylation using sodium hydride as base dipolar aprotic solvents like DMF or DMSO are necessary.22 During the benzylation a reversible TDS rearrangement between C-la and C-2a of the lactose occurs.23 First deprotonation with NaH leads to C-2a-oxide 44 formation and then to the rearrangement. 

Among the ethers of prolinol, (5)-2-methoxymethylpyrrolidinc [SMP, (S)-10] has found most applications. It is readily prepared from prolinol by the normal sodium hydride/iodo-methane technique9,13 (sec also Section 2.3. for O-alkylations of other amino alcohols) and is also commercially available. An improved synthesis from proline avoids the isolation of intermediates and gives the product (which is highly soluble in water) by continuous extraction14. SMP has been used as the lithium salt in deprotonation and elimination reactions (Section C.) and as an auxiliary for the formation of chiral amides with carboxylic acids, which in turn can undergo carbanionic reactions (Sections D.l.3.1.4., D.l. 1.1.2.. D.l. 1.1.3.1., in the latter experimental procedures for the formation of amides can be found). Other important derivatives are the enamines of SMP which are frequently used for further alkylation reactions via enolates (Sections D.l.1.2.2.. where experimental procedures for the formation of enamines are... 

Many different types of bases are used in organic chemistry. Common inorganic bases include the anions of weak bases such as water and ammonia (OH and NH2 ). Similar deprotonation of alcohols leads to the alkoxide bases (RO ). Methoxide (MeO ), ethoxide (EtO ), and ferf-butoxide (Me3C-0 ) are very common and are often used in the alcohol solvents from which they were made (methoxide in methanol, tert-butoxide in ferf-butanol, etc.). The bases used to deprotonate water (p fa = 15.8) or alcohols (pATa 18) are sodium hydride (NaH), potassium hydride (KH), sodium and potassium hydroxide (NaOH, KOH), sodium metal (Na°),... 

Oxygen Acids (Alcohol Deprotonation). Sodium hydride may be used as a base in the Williamson ether s)uithesis in neat benzyl chloride, in DMSO, or in THE (eq 2)f Phenols may also be deprotonated and alkylated in THE. ... 

Deprotonation of vinylsilane-allylic alcohols using sodium hydride in HMPA is followed by an essentially quantitative C —> O silicon migration (eq 7). ... 

Compare, for example, these typical conditions used to make a methyl ether and a tert-butyl ether. The methyl ether is made, as you saw on p. 340, using methyl iodide in an 8 2 reaction. It needs a good nucleophile, so the alcohol is deprotonated to make an alkoxide with sodium hydride in DMF, which, as you saw on p. 345, is a good solvent for 8 2 reactions. The fert-butyl ether on the other hand is made simply by stirring the alcohol with fcrf-butanol and a little acid. No base is needed, and the reaction proceeds rapidly to give the fcrf-butyl ether. 

The diazoketoester 20 undergoes cyclopropanation to the unstable pentacycle 6 (major product) when added dropwise to a solution of copper(ll)bis-salicylalde-hyde-/-butylimine in toluene, involving the intermediate carbene 7. Sodium boro-hydride reduces 6 in methanol solution to the secondary alcohol which is, for protection, converted to the benzyleflier 21 by Williamson synthesis involving deprotonation to the alcoholate by sodium hydride and 0-alkylation by benzyl-bromide so that diisobutylaluminumhydride (DIBAH) reduces the i-butylester in 21 to the primary alcohol 22 in dichloromethane. 

Sodium hydride Is a good base, and deprotonates the alcohol alkylation with Mel, via a nucleophilic substitution mechanism, gives the final ether product (Williamson ether synthesis). 

Sodium hydride is a strong base it readily deprotonates the alcohol function of phenol to generate a phenoxide anion. This anion then initiates an Sfj2 reaction at the electrophilic carbon of the chloroether. 

A strong base can be used to deprotonate the alcohol. A commonly used base is sodium hydride (NaH), because hydride (H ) deprotonates the alcohol to generate hydrogen gas, which bubbles out of solution ... 

Alcohols are commonly deprotonated with either sodium hydride (NaH) or an alkali metal (Na, Li, or K). 

The ability of nucleophilic substitution to provide either 2,6-cis or 2,6-trans THP has been exploited in the synthesis of several natural products. Williams and coworkers reported the formation of both the A and B ring of leucascandrolide A by nucleophilic substitution (Scheme 14) [35]. Both examples relied oti a methanesulfonate leaving group and secondary alcohol nucleophile. Subjecting mesylate 44 (or 46) to sodium hydride deprotonation followed by heating resulted in THP product 45 (or 47) in 75 % yield as a single diastereomer. 

The resting state of the propanoate catalysts may well be an acyl complex [60,61], while the attack of alcohol at the acylpalladium complex is considered to be the rate-determining step. It is probably more precise to say that fast preequilibria exist between the acyl complex and other complexes en route to it and that the highest barrier is formed by the reaction of alcohol and acylpalladium complex. The precise course of the reaction is still not known presumably deprotonation of the coordinating alcohol and the migratory elimination are concerted processes, accelerated by the steric bulk of the bidentate ligand. Toth and Elsevier showed that the reaction of an acetylpalladium complex and sodium methoxide is very fast and occurs already at low temperature to give methyl acetate and a palladium(I) hydride dimer [46]. 

Osmium pentacarbonyl is a convenient precursor to other osmium carbonyl complexes. Hydrogenation gives the dihydride OsH2(CO)4. This hydride is not acidic with a p/fa of 18.5 but it can be deprotonated by strong bases to give [OsH(CO)4] and reduced by sodium (Scheme 23). Substitution of CO on Os(CO)5 by trialkyl or triarylphosphines, arsines, or stibenes gives Os(CO)4L or Os(CO)3L2. Other carbonyl phosphine complexes result from the reduction of osmium halides by alcohols in the presence of the tertiary phosphine. 

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