Alcohols protonation with sulfuric acid

An example for Uquid phase chemistry with solid phase woikup has recently been published. In this case, a quinoline-carboxylic ester was transesterifled with an appropriate bromobenzyl alcohol. The Suzuki coupling with a boronic acid derivative proceeded smoothly and the quinoline handle was cleaved off. The advantage of this method lies in the ease of purification since the quinoline could be sequestered from the reaction mixture by protonation with sulfuric acid and recrystallization. - ... 

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

One example is to separate mono- and dicarboxylic acids from alcohols and carbohydrates using a cation resin in the H form with sulfuric acid as the eluate. Strong acids are highly ionized and elute at the void volume of the column, whereas the nonionic alcohols and carbohydrates, which are completely protonated, are neutral and enter the resin. They generally emerge from the resin in the order of the smallest molecule first. 

In this step, an acid—base reaction, a proton is rapidly transferred from the acid to one of the unshared electron pairs of the alcohol. In dilute sulfuric acid the acid is a hydronium ion in concentrated sulfuric acid the initial proton donor is sulfuric acid itself. This step is characteristic of all reactions of an alcohol with a strong acid. 

Acid—Base Chemistry. Acetic acid dissociates in water, pK = 4.76 at 25°C. It is a mild acid which can be used for analysis of bases too weak to detect in water (26). It readily neutralizes the ordinary hydroxides of the alkaU metals and the alkaline earths to form the corresponding acetates. When the cmde material pyroligneous acid is neutralized with limestone or magnesia the commercial acetate of lime or acetate of magnesia is obtained (7). Acetic acid accepts protons only from the strongest acids such as nitric acid and sulfuric acid. Other acids exhibit very powerful, superacid properties in acetic acid solutions and are thus useful catalysts for esterifications of olefins and alcohols (27). Nitrations conducted in acetic acid solvent are effected because of the formation of the nitronium ion, NO Hexamethylenetetramine [100-97-0] may be nitrated in acetic acid solvent to yield the explosive cycl o trim ethyl en etrin itram in e [121 -82-4] also known as cyclonit or RDX. 

Diethyl ether and other simple symmetrical ethers are prepared industrially by the sulfuric acid-catalyzed dehydration of alcohols. The reaction occurs by SN2 displacement of water from a protonated ethanol molecule by the oxygen atom of a second ethanol. Unfortunately, the method is limited to use with primary alcohols because secondary and tertiary alcohols dehydrate by an El mechanism to yield alkenes (Section 17.6). 

Halide formation proceeds at a useful rate only in the presence of strong acid, which can be furnished by excess hydrogen bromide or, usually and more economically, by sulfuric acid. The alcohol accepts a proton from the acid to give an alkyloxonium ion, which is more reactive in subsequent displacement with bromide ion than the alcohol (by either SN2 or SN1 mechanisms) because H20 is a better leaving group than eOH ... 

This is the reverse of acid-catalyzed hydration of alkenes discussed previously (Section 10-3E) and goes to completion if the alkene is allowed to distill out of the reaction mixture as it is formed. One mechanism of dehydration involves proton transfer from sulfuric acid to the alcohol, followed by an E2 reaction of hydrogen sulfate ion or water with the oxonium salt of the alcohol ... 

The protection of the amine as a hydrochloride, allows the selective oxidation of the alcohol with 62% yield. However, the protection of the amine is not complete by protonation, because the DMSO present in the medium is basic enough to compete as proton scavenger. A better protection of the amine by the addition of ca. 0.5 eq. of concentrated sulfuric acid, as an extra proton source, allows to increase the yield to 78%. 

Finch and Symons,87 on reinvestigation of the absorption of aliphatic alcohols and alkenes in sulfuric acid solution, showed that the condensation products formed with acetic acid (used as solvent for the precursor alcohols and alkenes) were responsible for the spectra and not the simple alkyl cations. Moreover, protonated mesityl oxide was identified as the absorbing species in the system of isobutylene, acetic acid, and sulfuric acid. 

Table XIII summarizes proton chemical shift data for the three carbonium ion salts (Via, b, and c) and for the alcohols from which they were prepared by treatment with concentrated sulfuric acid or trifluoroacetic...

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