1,4-butane diol alternatives

The standard diol chain extender used for the synthesis of PU elastomers was 1,4-butane diol (BDO). Products from this type of material, as a generalization, have inferior properties to aromatic diamine curatives and various alternatives have been introduced over the last few years to attempt to simulate the properties of the urethane diamine cure or to produce special effects. Examples of these are shown below ... 

Butandiol was used as a smart cosubstrate to promote NAD(P)H reductase-dependent reactions. 7-Butyrolactone, the product of two successive essentially irreversible enzyme-catalyzed oxidations, is thermodynamically stable and chemically inert that drives the reaction strongly in the direction of substrate reduction. The authors examined the reduction of NAD(P)+ by 1,4-butanediol with 12 commercially available reductases, 8 of which successfully accepted the diol substrate. In the reduction of cinnamaldehyde with horse liver dehydrogenase, both the initial rate and maximum conversion were higher with 1,4-butan-diol than with alternative sacrificial reductants such as iso-propanol or ethanol (Scheme 6.33) [48]. 

Microorganisms have also been developed to produce alternative products, such as lactic acid [65], propane-1,3-diol [67], 3-hydroxypropionic acid [68], butane-2,3-diol [69] and numerous other intermediates. For instance, bacteria such as the Clostridium acetobutylicum ferment free sugars to C4 oxygenates such as butyric acid or butanol. They form the C4 oxygenates by Aldol condensation of the acetaldehyde intermediates. The Weizmann process exploits this property to ferment starch feedstock anaerobically at 37 °C to produce a mixture of w-butanol, acetone and ethanol in a volume ratio of 70 25 5 [3],... 

As an alternative route to the sesquicarane-type sesquiterpenoids, Hortmann and Ong have examined the carbanionic opening of the epoxy-ester (70) derived from perillaldehyde (71). The two products of this reaction are (72) and (73) in the ratio 3 1. Further elaborations of these two compounds have still to be carried out. Plattner and Rapoport have now reported the preparation of both (+)- and (— )-sirenin. This was accomplished by preparative g.l.c. separation of the two diastereoisomeric pairs of ketals derived from the synthetic ketone (74) and D-( —)- and L-( -1- )-butane-2,3-diols. Synthetic procedures for the conversion of racemic (74) into both racemic sirenin and racemic sesquicarene had already been developed. Furthermore, these authors have firmly established by chemical correlation and c.d. studies that naturally-occurring sirenin and sesquicarene have the same absolute stereochemistry, i.e. (75) and (76) respectively. 

Isopropylidene (acetonides) and benzylidene derivatives are the most commonly used acetals for the simultaneous protection of 1,2- and 1,3-diols in carbohydrate and nucleoside chemistry [123]. Cyclohexylidene acetals are occasionally used, most often as an alternative to benzylidene acetals. Protection using cyclohexane- 1,2-diacetals or the related butane-2,3-diacetals represents a new approach which has proved its value in complex oligosaccharide synthesis [124]. 

Lowering the water-activity (concentration) of the system by addition of water-miscible organic cosolvents. In this respect, polyhydroxy compounds such as glycerol or butane-1,4-diol have been shown to conserve enzyme activity better than the solvents which are more commonly employed, such as DMF, DMSO, ethanol, acetone, or acetonitrile [305]. Alternatively, peptide synthesis may also be performed with neat reactants - i.e., in the absence of solvents [306]. 

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