Dehydration 3-pentanol

At this point, the Grignard reaction is our most powerful method for assembling a carbon skeleton, and Grignards can be used to make primary, secondary, and tertiary alcohols (Section 10-9). The secondary alcohol 3-ethyl-2-pentanol has its functional group on C2, and the tertiaiy alcohol 3-ethyl-3-pentanol has it on C3. Either of these alcohols can be synthesized by an appropriate Grignard reaction, but 3-ethyl-2-pentanol may dehydrate to give a mixture of products. Because of its symmetry, 3-ethyl-3-pentanol dehydrates to give only the desired alkene, 3-ethyl-2-pentene. It also dehydrates more easily because it is a tertiary alcohol. 

Few detailed studies of olefinic dehydration products have been reported. Rapoport ei al. (105) found cis- and major products from n-pentanol dehydration over NaX only traces of 2-methyl-1-butene and 2-methyl-2-butene were reported. Thus, it is evident that double bond isomerization has accompanied or followed the dehydration reaction. Several authors (99,101,106) have suggested that diffusion processes may be rate controlling, or at least of some significance, in zeolite-catalyzed dehydration reactions. Molecular-shape selective alcohol dehydration (7) was discussed earlier. 

In addition to being regioselective alcohol dehydrations are stereoselective A stereo selective reaction is one m which a single starting material can yield two or more stereoisomeric products but gives one of them m greater amounts than any other Alcohol dehydrations tend to produce the more stable stereoisomer of an alkene Dehydration of 3 pentanol for example yields a mixture of trans 2 pentene and cis 2 pentene m which the more stable trans stereoisomer predominates... 

Dehydration of 2 2 3 4 4 pentamethyl 3 pentanol gave two alkenes A and B Ozonolysis of the lower boiling alkene A gave formaldehyde (H2C=0) and 2 2 4 4 tetramethyl 3 pentanone Ozonolysis of B gave formaldehyde and 3 3 4 4 tetramethyl 2 pentanone Identify A and B and suggest an explanation for the formation of B in the dehydration reaction... 

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" ... 

Dehydration of 1-pentanol or 2-pentanol to the corresponding olefins has been accompHshed, in high purity and yields, by vapor-phase heterogeneous catalyzed processes using a variety of catalysts including neutral gamma —Al Og catalyst doped with an alkah metal (23), zinc aluminate (24,25), hthiated clays (26), Ca2(P0 2 montmorillonite clays (28). Dehydration of 2-methyl-1-butanol occurs over zinc aluminate catalyst at... 

C to give the expected 2-methyl-1-butene in high selectivites (24). The AI2O2 catalyzed process can be optimized to give di- -pentyl ether as the exclusive product (23). Dehydration of 1-pentanol over an alkah metal promoted AI2O2 catalyst at 300—350°C provides 1-pentene at selectivities of 92% (29,30). Purification produces polymerization grade (99.9% purity) 1-pentene. A flow chart has been shown for a pilot-plant process (29). 

Ethanol [64-17-5] M 46.1, b 78.3 , d 0.79360, d 0.78506, n 1.36139, pK 15.93. Usual impurities of fermentation alcohol are fusel oils (mainly higher alcohols, especially pentanols), aldehydes, esters, ketones and water. With synthetic alcohol, likely impurities are water, aldehydes, aliphatic esters, acetone and diethyl ether. Traces of benzene are present in ethanol that has been dehydrated by azeotropic distillation with benzene. Anhydrous ethanol is very hygroscopic. Water (down to 0.05%) can be detected by formation of a voluminous ppte when aluminium ethoxide in benzene is added to a test portion. Rectified... 

Solution 2-Methyl-3-pentanol, an open-chain alcohol, has M+ = 102 and might be expected to fragment by o- cleavage and by dehydration. These processes would lead to fragment ions of m/z = 84, 73, and 59. Of the three expected fragments, dehydration is not observed (no m/z = 84 peak), but both a clea iges take place (m/z = 73, 59). 

The liquid-phase dehydration of 1-hexanol and 1-pentanol to di-n-hexyl ether (DNHE) and di-n-pentyl ether (DNPE), respectively, has been studied over H-ZSM-5, H-Beta, H-Y, and other zeolites at 160-200°C and 2.1 MPa. Among zeolites with a similar acid sites concentration, large pore H-Beta and H-Y show higher activity and selectivity to ethers than those with medium pores, although activity of H-ZSM-5 (particularly in 1-pentanol) is also noticeable. Increased Si/Al ratio in H-Y zeolites results in lower conversion of pentanol due to reduced acid site number and in enhanced selectivity to ether. Selectivity to DNPE is always higher than to DNHE... 

Keywords Alcohol dehydration, 1-pentanol, 1-hexanol, linear ethers, zeolites. 

In spite of the fact that alumina is an excellent and widely used catalyst for the dehydration of alcohols, there is no agreement in the literature with regard to the mechanism of this reaction or the nature of the olefinic products. For example, 1-alkenes have been obtained from primary alcohols such as 1-butanol (19-22), 1-pentanol (23), 1-hexanol (24-26), 1-heptano (27), and 1-octanol (25) but mixtures of olefins differing in the position of the double bond (13, 26, 28) or even in the carbon skeleton (29) have been reported from other primary alcohols. 

Dehydration of 2-Butanol and 2-Pentanol over Various Aluminas at HLSV = 0.5... 

The dehydration of the two alcohols over alumina catalyst in the presence of piperidine was studied by Pillai and Pines [84). The experimental results which are given in Table X indicate that, although carbonium ion mechanism can interpret the products obtained from the tertiary alcohols, another mechanistic path has to prevail in order to account for the formation of the various dehydration products from 3,3-dimethyl-2-pentanol. The mechanism, as proposed above for the dehydration of 3,3-dimethyl-2-butanol, would also explain the hydrocarbons formed from the dehydration of 3,3-dimethyl-2-pentanol. 

Phenylpiperidine has been prepared by warming aniline with 1,5-dibromopentane 4,8 heating 5-anilino-l-bromopentane 6 the dehydration of 5-anilino-l-pentanol over alumina 7 the electrolytic reduction of N-phenylglutarimide 8 the catalytic hydrogenation of l-phenyl-3-hydroxypyridinium chloride 9 the action of bromobenzene on piperidine in the presence of lithium 10 the reaction of fluorobenzene, 1-methylpiperidine, and phenyl-lithium 11 the action of diphenylsulfone on piperidine in the presence of sodamide 12 the diazotization and deamination of l-(2-aminophenyl)piperidine 13 and of l-(4-aminophenyl)piperidine 14 and the present method.18... 

Tetralins indanes. P205 can be used for cyclodehydration for substrates such as 1-aryl-l-pentanols or 2-aryl-2-hexanols. In the case of secondary alcohols, yields are sometimes improved by dehydration with TsOH to a styrene followed by cyclization with P2O5.1 The product of the second example is a known sesquiterpene, calamenene. 

SAMPLE SOLUTION (a) The hydrogen and the hydroxyl are lost from adjacent carbons in the dehydration of 3-ethyl-3-pentanol. 

The dehydration of 2-pentanol in the presence of a strong acid and heat results in a(n) ... 

Pentanol can undergo dehydration in two different directions, giving either 1-pentene or 2-pentene. 2-Pentene is formed as a mixture of the cis and trans stereoisomers. 

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