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ChemicalBook CAS DataBase List 1,6-Hexanediol
629-11-8

1,6-Hexanediol synthesis

12synthesis methods
1,6-Hexanediol is produced industrially by the catalytic hydrogenation of adipic acid or of its esters. Mixtures of dicarboxylic acids and hydroxycarboxylic acids with C6 components formed in other processes (e.g., in cyclohexane oxidation) are also used. Esterifification of "distillation heavies" with lower alcohols is often carried out before hydrogenation. The acids are hydrogenated continuously at 170-240 ℃ and at 15.0-30.0 MPa on a suitable catalyst either in a trickle-flflow (downflflow) or a bubble-flflow (upflflow) fifixed-bed reactor. The reactor temperature is controlled by circulating part of the reactor discharge. The hydrogen required for the hydrogenation is fed together with the recycle gas through the recycle gas compressor to the reactor. Side products of the synthesis are alcohols, ethers, diols, and esters. Pure 1,6-hexanediol is obtained by fractional distillation of the crude reactor discharge. For the hydrogenation of dicarboxylic acids, catalysts containing cobalt, copper, or manganese are suitable. For the hydrogenation of esters, catalysts such as copper chromite or copper with added zinc and barium are used as "full catalysts" or on inert carriers. Ruthenium, platinum, or palladium on inert supports can also be used. Gas-phase hydrogenation of esters of adipic or 6-hydroxyhexanoic acid can be carried out at 1-7 MPa. Both acids and esters also may be hydrogenated using suspended catalysts. Oligomeric esters of the product diol and adipic acid can also be hydrogenated.
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Yield:629-11-8 98%

Reaction Conditions:

with C21H35BrMnN2O2P;hydrogen;potassium hydride in toluene at 100; under 15001.5 Torr; for 36 h;

Steps:

16

Hydrogenation of 1 mmol of hexyl hexanoate under 20 bar at 100°C in toluene, resulted in 99% yield of hexanol (Entry 1). Under the same conditions ethyl butyrate was hydrogenated to give 98% yield of butanol and 91 % yield of ethanol after 50 hours (Entry 2). When the reaction was performed at shorter reaction time (22 hours, Entry 2bis), small amounts of ethyl acetate and butyl butanoate were also formed, attributed to a transesterification reaction with the formed ethanol and butanol. Cyclohexylmethyl acetate gave 99% yield of cyclohexylmethanol and 60% yield of ethanol (Entry 3), and no transesterification products were observed. Hydrogenation of the secondary aliphatic ester heptan-2-yl acetate resulted in 98% yield of heptane-2-ol and 57% yield of ethanol (Entry 4). Ethyl 3-phenylpropanoate was smoothly hydrogenated, rendering 99% yield of 3-phenylpropan-l-ol and 70% yield of ethanol after 21 hours (Entry 5). Similarly, ethyl 3- phenylpropanoate gave 99% yield of phenyknethanol and 74% yield of butanol after 22 hours (Entry 6). In order to get full hydrogenation of benzyl benzoate longer reaction time was needed (43 hours, 99% yield benzyl alcohol, Entry 7). Similarly, methyl benzoate gave 96% yield of benzyl alcohol and 63 % of methanol after 50 hours (Entry 8). ε-Caprolactone was smoothly and quantitatively hydrogenated to 1 ,6-hexanediol (99% yield, Entry 9). The activated benzyl trifluoroacetate gave 99% yield of benzyl alcohol and 78% of 2,2,2- trifluoroethanol (Entry 10), and no secondary products where observed. Gratifyingly, allyl trifluoroacetate gave 97% yield of 2,2,2-trifluoroethanol and 96% of allyl alcohol (Entry 1 1), showing high chemoselectivity to ester hydrogenation over C=C hydrogenation. Hydrogenation of ethyl 4-isocyano-benzoate required an increase of precatalyst loading to 3%, probably due to competing nitrile coordination, and resulted in 61 % yield of (4-isocyanophenyl)methanol and 66% yield of ethanol, with no hydrogenation of the nitrile group detected (Entry 12).

References:

WO2017/137984,2017,A1 Location in patent:Paragraph 00352-00353

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