Dehydration elimination reaction

The E1 Elimination Reaction Dehydration of 2-Butanol to Yield 1 -Butene, trans-2-Butene, and cis-2-Butene... 

SYNTHETICALLY USEFUL ELIMINATION REACTIONS DEHYDRATION OF AN ALCOHOL VIA AN El PROCESS... 

The first task was to prepare the chiral sulfoxide. The synthesis began with the conversion of methyl propionate (144) to keto-sulfide 145. Enzymatic reduction of the ketone using Baker s Yeast gave 146 with decent enantiose-lectivity. A directed oxidation of the sulfide provided an unequal mixture of sulfoxides 147 and 148 (and presumably minor amounts of material derived from the 4-5% of ent- 46 present in the starting material) from which 148 could be isolated in 50% yield. Dehydration of the alcohol provided 149 (along with some of the Z isomer). Notice that Mori decided to place the alcohol beta to the sulfoxide in the precursor of 149. There might be a number of reasons for this, but one is that it facilitated the elimination reaction (dehydration) because of the electron-withdrawing properties of the sulfoxide. 

Zaitsev s rule as applied to the acid catalyzed dehydration of alcohols is now more often expressed in a different way elimination reactions of alcohols yield the most highly substituted alkene as the major product Because as was discussed in Section 5 6 the most highly substituted alkene is also normally the most stable one Zaitsev s rule is sometimes expressed as a preference for predominant formation of the most stable alkene that could arise by elimination... 

When optically pure 2 3 dimethyl 2 pentanol was subjected to dehydration a mixture of two alkenes was obtained Hydrogenation of this alkene mixture gave 2 3 dimethylpentane which was 50% optically pure What were the two alkenes formed in the elimination reaction and what were the relative amounts of each" ... 

Butadiene is an industrial chemical and is prepared by dehydrogena tion of butane Elimination reactions such as dehydration and dehydro halogenation are common routes to alkadienes... 

Other Syntheses. Acryhc acid and other unsaturated compounds can also be made by a number of classical elimination reactions. Acrylates have been obtained from the thermal dehydration of hydracryhc acid (3-hydroxypropanoic acid [503-66-2]) (84), from the dehydrohalogenation of 3-halopropionic acid derivatives (85), and from the reduction of dihalopropionates (2). These studies, together with the related characterization and chemical investigations, contributed significantly to the development of commercial organic chemistry. 

The dehydration of alcohols is an important elimination reaction that takes place under acidic rather flian basic conditions. It involves an El mechanism." The function of the acidic reagent is to convert the hydroxyl group to a better leaving group by protonation ... 

The use of mesyl chloride for the dehydration of C-11 alcohols has already been mentioned, and mesylates can certainly be intermediates at least in the a-series. The preference for a coplanar trans arrangement is demonstrated by the well-known elimination reactions of tosylates of epimeric 20-alcohols (ref. 185, p. 616), although this does not restrict the usefulness of the reaction, and in some cases (sulfonates of 1 la-alcohols, for example) cw-elimination occurs (ref. 216, p. 293 ref. 224, 225, 226). 

The two most common elimination reactions arc dehydroUalogenalion—the loss of HX from an alkyl halide—and dehydration—(he loss of water from an alcohol. Dehydrohalogenation usually occurs by reaction of an alkyl halide with strong base such as potassium hydroxide. For example, bromocvclohexane yields cyclohexene when treated with KOH in ethanol solution. 

Alkenes are generally prepared by an elimination reaction, such as dehydrohalo-genation, the elimination of FIX from an alkyl halide, or dehydration, the elimination of water from an alcohol. 

All three elimination reactions--E2, El, and ElcB—occur in biological pathways, but the ElcB mechanism is particularly common. The substrate is usually an alcohol, and the H atom removed is usually adjacent to a carbonyl group, just as in laboratory reactions. Thus, 3-hydroxy carbonyl compounds are frequently converted to unsaturated carbonyl compounds by elimination reactions. A typical example occurs during the biosynthesis of fats when a 3-hydroxybutyryl thioester is dehydrated to the corresponding unsaturated (crotonyl) thioester. The base in this reaction is a histidine amino acid in the enzyme, and loss of the OH group is assisted by simultaneous protonation. 

The dehydration occurs by initial reaction of SOCl2 on the nucleophilic amide oxygen atom, followed by deprotonation and a subsequent E2-like elimination reaction. 

Problem 29.12 ls the pro-R or pro-5 hydrogen removed from citrate during the dehydration in step 2 of the citric acid cycle Does the elimination reaction occur with syn or anti geometry ... 

Claisen rearrangement, 1194-1195 dehydration, 622 elimination reactions, 393 oxidation, 625-626 radical reactions, 243-244 characteristics of, 162-164 comparison with laboratory reactions, 162-164 conventions for writing, 162. 190 energy diagram of, 161 reduction, 723-725 reductive animation, 932 substitution reactions, 381-383 Biological reduction, NADH and, 610-611... 

An elimination reaction is, in a sense, the reverse of an addition reaction. It involves the elimination of two groups from adjacent carbon atoms, converting a saturated molecule into one that is unsaturated. An example is the dehydration of ethanol, which occurs when it is heated with sulfuric acid ... 

Hydroxy-( , )-a,y-dienylsulfones are prepared by an analogous one-pot dehydration procedure via an elimination reaction of the corresponding cyclic carbonate [21]... 

Alcohols form alkenes in an elimination reaction when reacted with dehydrating agents. 

The geometry of the cis-alkylcyclohexanol is favorable for trans elimination since the hydroxyl and the neighboring trans hydrogen are coplanar, but this is not true for the l,i-trans isomer hence the molecular conformation has to flip over, to set the hydroxyl group in the axial position for the trans elimination to occur. This would require a few kilocalories of energy and for frans-lert-butylcyclohexanol it would be more difficult to achieve than for IroMs-methylcyclohexanol. It is, therefore, possible that the trans elimination from a boat conformation, or possibly even an epimerization from the trans to the cis isomer which then undergoes a trans elimination reaction. Such an epimerization was found to occur under conditions of dehydration of certain alcohols over alumina, as will be seen under 1,4-cyclohexanediol. The more facile elimination of the cis-i-tert-butylcyclohexanol system as compared with the trans system in solution was also reported in the literature 63). 

The formation of 1,9- and cis-1,2-octalin from ci5,cis-l-decalol is a clear indication of the dehydration by means of a trana elimination reaction ... 

The faster rate of dehydration of 2-ea o-bornanol over that of 2-endo-bornanol can be attributed in part to the anchimeric assistance of the C(l)-C(6) bonding electrons which are trans to the electrons bonding the OH group to C(2) carbon, as with solvolytic reactions 74), The occurrence of tricyclene as the primary product of dehydration of 2-ea o-bornanol can best be explained by an elimination reaction which takes place within the submicroscopioal pores of the aluminas. 

The dehydration to 1-butene proceeds most probably via a trans elimination reaction. The formation of 2-butenes, which were the primary products of reaction, can best be explained by a removal of hydrogen from a y-carbon atom, as was indicated in the case of menthols ... 

There is a strong parallel between elimination reactions in solution and the dehydration of alcohols over alumina. The trans elimination reactions and the anchimeric assistance of alcohols over aluminas suggest that the dehydration must occur within either the submicroscopical pores, or crevices, or channels of the aluminas. The aluminas therefore must surround the alcohol molecules providing acid sites to act as proton donors or electron acceptors and basic sites to act as proton acceptors or electron donors. For that reason the aluminas seem to act as solvating agents and therefore may be considered as a pseudosolvents for dehydration reactions. 

As has been mentioned previously, one is most likely to find analogies to catalytic reactions on solids with acidic and/or basic sites in noncatalytic homogeneous reactions, and therefore the application of established LFERs is safest in this field. Also the interpretation of slopes is without great difficulty and more fruitful than with other types of catalysts. The structure effects on rate have been measured most frequently on elimination reactions, that is, on dehydration of alcohols, dehydrohalogenation of alkyl halides, deamination of amines, cracking of the C—C bond, etc. Less attention has been paid to substitution, addition, and other reactions. 

An inspection of Table II (26,40-64) shows that, in most cases, the slopes have negative values, some being highly negative. There may be two reasons for these unusual magnitudes. Elimination reactions bring the problem of the division of the reacting molecule into the reaction center and the substituent. When, for example, the dehydration of aliphatic alcohols is studied... 

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