1-Octanol, dehydration

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. 

As mentioned earlier, two side reactions are present Octene is formed to a low extent (<2 %), and this might occur by dehydration of the 1-octanol or by splitting of an ester. Due to the small amounts, neither the mechanism of octene formation was further investigated, nor the principally possible isomerization of octene and subsequent formation of secondary esters or ethers. 

In fact, whenever the primary carbonium ion is formed from the proper substrate, ring expansion is observed this is the case in the acid-catalyzed dehydration of 2-hydroxymethylbicyclo[2.2.1]heptane (23), producing a mixture of 2.5% methylenebicyclo[2.2.1]heptane (7), 87% bicyclo[3.2.1]-2-octene (5), and 10% bicyclo[3.3.0]-2-octene (6) and in the nitrous acid deamination of 2-aminomethylbicyclo[2.2.1]-heptane to bicyclo[3.2.1]- and bicyclo[2.2.2]octanols 30). 

The passage from bicyclo[2.2.2]octane structures to the isomeric bicyclo[3.2.1]octanes is irreversible for all practical purposes in the CsHiz and C9H14 series (it was not investigated in the CioHie series) and this conclusion is substantiated by other facts the acid-catalyzed dehydration of 2-methylbicyclo[3.2.1]-2-octanols and 3-methylbicyclo-[3.2.1]-3-octanols gives small quantities of methylbicyclo[2.2.2]octenes 30), while the acid-catalyzed hydration of bicyclo[2.2.2]-2-octene forms the bicyclo[3.2.1]-2-octanol 27) the nitrous acid deamination of 2-aminobicyclo[2.2.2]-5-octene goes to bicyclo[3.2.1]octenols 31) and the solvolysis of bicyclo[2.2.2]-5-octen-2-ol esters to bicyclo[3.2.1]octenols 32). 

ALCOHOL terc-BUTILICO (Spanish) (75-65-0) see tert-butyl alcohol. ALCOHOL C-8 (111-87-5) see octanol. ALCOHOL C-9 (143-08-8) see 1-nonanol. ALCOHOL 0-10(112-30-1) see n-decanol. ALCOHOL, DEHYDRATED or ALCOHOL, DENATURED (containing an additive used to make it unfrt for use as a beverage) or ALCOHOL ETILICO (Spanish) (64-17-5) see ethanol. 

Boric acid is a mild dehydrating agent suitable for removal of water from some primary, secondary, or tertiary alcohols. Since the acid and the alcohol form first a trimeric metaboric ester, which then regenerates the boric acid when it decomposes to the olefin,36 the reaction is somewhat similar to pyrolysis of carboxylic esters but the boric acid dehydration occurs at appreciably lower temperatures (250-300°). Olefins are readily obtained by heating approximately molar equivalents of boric acid and 1-octanol, 1-heptanol, 1-hexanol, (—)-menthol, cyclohexanol, or 5cyclohexane-methanol, and cyclobutanemethanol.38... 

While the aqueous phase of the n-octanol/water system contains nearly no octanol at equilibrium, the octanol phase dissolves an appreciable amount of water (2.3 mol-l , corresponding to a molar ratio of n-octanol/water 4/1) therefore, polar groups need not be dehydrated on their transfer from the aqueous phase to the organic phase. 

An open-vessel approach using a Dean-Stark trap placed outside the micro-wave cavity has been used to facilitate esterifications of acetic acid and acid-catalyzed dehydrations of octanol on the 2-6 mol scale. Open-vessel microwave heating is ideal for high-temperature distillations compared to conventional approaches due to the rapid noncontact heating possible, making the procedure easy and safe. 

The use of secondary alcohols as reductants for DODH was first reported by Elhnan, Bergman, and coworkers, who employed Re-carbonyl compounds, e.g., Re2(CO)io, as pre-catalysts under aerobic conditions (Scheme 16) [36]. Optimized conditions used the glycol substrate with the mono-alcohol as the solvent, e.g., 3-octanol, at 150-175°C, with 1-2.5 mol% Re2(CO)io and TsOH as a co-catalyst (2-5 mol%). Good yields of the olefin (50-84%) were obtained with representative glycols. The sy -3,4-decanediol was converted highly selectively to trans-3-decene, implicating a sy -eUmination process in the diol to olefin conversion (Scheme 17). Erythritol was converted moderately efficiently to 2,5-dihydrofuran (62% yield), presumably the result of initial 1,4-diol dehydration followed by DODH of the THF-diol intermediate. The nature of the active catalyst was unknown at the time, but was speculated to be an oxidized Re species. 

Alcohols and linear or cyclic aliphatic ethers can be carbonylated to mono-or dicarboxylic acids using Ni(CO)4 in the presence of a co-catalyst, e.g., Cul or Nil2 15). Reaction probably proceeds via olefinic intermediates formed by dehydration of the alcohol or ether. Thus, 1-octanol and 2-octanol both yield the same acid, 2-methyloctanoic 15d). 

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