Butanediol-water, dehydration

Pinacol rearrangement is a dehydration of a 1,2-diol to form a ketone. 2,3-drmethyl-2,3-butanediol has the common name pinacol (a symmetrical diol). When it is treated with strong acid, e.g. H2SO4, it gives 3,3-dimethyl-2-butanone (methyl r-butyl ketone), also commonly known as pinacolone. The product results from the loss of water and molecular rearrangement. In the rearrangement of pinacol equivalent carbocations are formed no matter which hydroxyl group is protonated and leaves. 

Fig. 14 Modified van Krevelen plot for the dehydration of sorbitol (after hydrogenation of glucose), lactic acid, 1,4-butanediol, and n-butanol. DH = dehydration, HG = hydrogenation. The effect of hydration of an aldose (hemi-acetal formation with water) is also shown...

BASF have also introduced an ionic liquid process in which HCl is used to chlorinate 1,4-butanediol in a chloride ionic liquid [130]. This previously required the use of environmentally damaging and/or toxic chlorinating/dehydrating agents, such as COCI2, SOClj, PCI3, to prevent the formation of partially chlorinated or ether by-products (Scheme 2.7). Water is a by-product of this process and when its level exceeds 25 mol%, the ionic liquid must be refreshed and dried. 

Hunter SE, Ehrenberger CE, Savage PE. (2006). Kinetics and mechanism of telrahydrofuran synthesis via 1,4-butanediol dehydration in high-temperature water. JOrg Chem, 71,6229— 6239. 

PBT is produced from both terephthalic acid and dimethyl terephtha-late with 1,4-butanediol. Most commercial PBT grades are initially developed with DMT because the TPA process generates a larger amount of tetrahydrofuran by-product and DMT is easier to purify than the TPA. Also, the higher solubility of the DMT allows a handling convenience and faster reaction rates in the transesterification stage with lower boiling point of methanol rather than water. The DMT process produces lower amounts of THF, a by-product formed by the irreversible acid-catalyzed dehydration of 1,4-butanediol, compared to the TPA process. However, in the commercial continuous process, more and more processes have shifted to TPA as the feedstock. In the newly developed TPA process. 

The enzymatic synthesis of a telechelic polyester having a hydroxy group, a prepolymer of polyurethane, at both ends was reported [38]. The lipase CA-catalyzed polymerization of adipic acid with an excess of 1,4-butanediol was performed imder reduced pressure. The content of water formed by dehydration polymerization greatly affected the enzyme activity and polymerization rates. 

A) and butane-1,4-diol (B), after 4 hours a predominant amount of hydroxy terminated oligomers BAB and B(AB)2as well as butanediol and adipic acid (insoluble) were observed. The proposed oligomerisation process pathway was that adipic acid (A) acylates the enzyme the acyl-enzyme complex is attacked by butane-1,4-diol (B) releasing AB. AB then acylates the enzyme via the acid terminus and the enzyme-AB complex is attacked by B to give BAB which does not react with the enzyme but, in due course, attacks an enzyme-AB complex to give B(AB)2. The continuation of this cycle gives B(AB) . Kobayashi and co-workers [24-26] reported the dehydration polymerisation of diacids and diols to form polyester in water with use of lipase catalysts. 

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