Alkenes from alkene alcohols

This pathway is consistent with the loss of the OH and y hydrogen (n = 1) or 8 hydrogen (n = 2) the ring structure is not proved by the observations and is merely one possible structure for the product radical cation. The M - 18 peak is frequently exaggerated by thermal decomposition of higher alcohols on hot inlet surfaces. Elimination of water, together with elimination of an alkene from primary alcohols, accounts for the presence... 

The direct catalyzed or uncatalyzed oxidation of alkanes with oxygen is an important reaction in the industrial production of carboxylic acids, hydroperoxides (for production of epoxides from alkenes), alcohols, ketones, or aldehydes [60],... 

Because an enol contains both a C=C and a hydroxy group, the name enol comes from alkene + alcohol. 

HALIDES, VINYL base-induced elimination 17-13 from alkene-alcohols 15-51... 

Alcohol, Thiol-Ketone). Examples of the synthetically important alkene metathesis reaction are mostly found in Section 209 (Alkenes from Alkenes). 

The above simple process cannot be applied to the preparation of the homo-logues a higher temperature is requir (di-n-amyl ether, for example, boils at 169°) and, under these conditions, alkene formation predominates, leading ultimately to carbonisation and the production of sulphur dioxide. If, however, the water is largely removed by means of a special device (see Fig. Ill, 57,1) as soon as it is formed, good 300 of ethers may be obtained from primary alcohols, for example ... 

The 4-hydroxy-1-alkene (homoallylic alcohol) 81 is oxidized to the hetni-acetal 82 of the aldehyde by the participation of the OH group when there is a substituent at C3. In the absence of the substituent, a ketone is obtained. The hemiacetal is converted into butyrolactone 83[117], When Pd nitro complex is used as a catalyst in /-BuOH under oxygen, acetals are obtained from homoallylic alcohols even in the absence of a substituent at C-3[l 18], /-Allylamine is oxidized to the acetal 84 of the aldehyde selectively by participation of the amino group[l 19],... 

The l,5-hexadien-3-ol derivatives 792 and 794 are cycli2ed to form the cyclo-pentadiene derivatives 793 and 795 by insertion of an alkene into -allylpalla-dium formed from allylic alcohols in the presence of trifluoroacetic acid (lO mol%) in AcOH[490],... 

Like alcohol dehydrations El reactions of alkyl halides can be accompanied by carbocation rearrangements Eliminations by the E2 mechanism on the other hand nor mally proceed without rearrangement Consequently if one wishes to prepare an alkene from an alkyl halide conditions favorable to E2 elimination should be chosen In prac tice this simply means carrying out the reaction m the presence of a strong base... 

Alkene synthesis via alcohol dehydration is complicated by carbocation rearrangements A less stable carbocation can rearrange to a more sta ble one by an alkyl group migration or by a hydride shift opening the possibility for alkene formation from two different carbocations... 

We now have a new problem Where does the necessary alkene come from Alkenes are prepared from alcohols by acid catalyzed dehydration (Section 5 9) or from alkyl halides by dehydrohalogenation (Section 5 14) Because our designated starting material is tert butyl alcohol we can combine its dehydration with bromohydrm formation to give the correct sequence of steps... 

Many aldehydes and ketones are made m the laboratory from alkenes alkynes arenes and alcohols by reactions that you already know about and are summarized m Table 17 1... 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

Water adds to alkenes to yield alcohols, a process called hydration. The reaction takes place on treatment of the alkene with water and a strong acid catalyst (HA) by a mechanism similar to that of HX addition. Thus, protonation of an alkene double bond yields a carbocation intermediate, which reacts with water to yield a protonated alcohol product (ROH2+). Loss of H+ from this protonated alcohol gives the neutral alcohol and regenerates the acid catalyst (Figure 7.2). 

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. 

Dehydration (Sections 7.1. 11.10, 17.6) The loss of water from an alcohol. Alcohols can be dehydrated to yield alkenes. 

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