Butanediols isomers

FIGURE 10.1 Molecular structures of different butanediol isomers... 

In order to demonstrate the use of laser flash photolysis in elucidation of the MDI based polyurethane photolysis mechanism, three polyurethanes, two aryl biscarbamate models, an aryl monocarbamate model, and an aromatic amine were selected. Two of the polyurethanes are based on MDI while the third is based on TDI (mixture of 2,4 and 2,6 isomers in 80/20 ratio). The MDI based polyurethanes all have the same basic carbamate repeat unit. The MDI elastomer (MDI-PUE) is soluble in tetrahydrofuran (THF). The simple polyurethane (MDI-PU) based on MDI and 1,4-butanediol is used in the tert-butoxy abstraction reactions since it does not contain a polyether backbone. (See page 47 for structures of polymers and models.)... 

It not tertiary, the product yield is lowered by transfer of the carbinol hydride ion to the aldehyde to produce a new alkoxide and an enolate ion. Thus, propylene oxide, after reductive cleavage with LDBB and trapping with isobutyraldehyde or p-anisaldehyde, provided 5-methyl-2,4-hexanediol in 40-50% yield or 1-p-anisyl-1,3-butanediol in 44% yield, respectively (in both cases about equal mixtures of diastereoisomers were obtained). The cyclohexene oxide-derived dianion, when trapped with isobutyraldehyde, gave 2-(1-hydroxy-2-methylpropyl)cyclohexanol in 71% yield as a mixture of only partially separable isomers in the ratio 15 11 39 35. 

Scheme 21) (92TL5597>. In cases where EjZ isomers of the product alkene are possible, the thermodynamically preferred isomer predominates <90SL479>. Electrochemical reduction of certain 1,3,2-dioxathiolane 2,2-dioxides also affords alkenes <84BCJ3160>. Reduction of the cis and trans isomers of 4,5-dimethyl-1,3,2-dioxathiolane 2-thione using Raney nickel afforded meso- and ( + )-2,3-butanediol, respectively <65JOC2696>. 

CH3C0CH(0H)CH3, C4H8O2, M, 88.11, / pioi.skPa 148 °C, df 1.0062, ng 1.4171, has a pleasant buttery odor and both of its optical isomers occur widely in nature. It is synthesized by partial oxidation of 2,3-butanediol and is obtained as a byproduct in the fermentation of molasses. It is used for flavoring margarine. 

According to de Kreuk the difference between the viscosity values of similar compounds (e.g. 1,3- and 1,2-propanediol dinitrates, 1,3- and 2,3-butanediol dinitrates) may be attributed to rotational isomerism. Free rotation makes possible the formation of trans isomers which according to this author should possess a higher viscosity. This would explain the relatively high viscosities of 1,3-propanediol and 1,3-butanediol dinitrates. 

The difference between the dipole moments of the pure substance and their value in benzene solution is (according to de Kreuk) due to the possible formation of a certain amount of trans rotation isomer in benzene. High values for pure 1,2-propanediol dinitrate and 2,3-butanediol dinitrate are due to the presence of a high proportion of the cis form in the pure liquids. 

Purity is determined by gas chromatography. Technical grade butenediol, specified at 95% minimum, is typically 96 to 98% butenediol. The cis isomer is the predominant constituent 2 to 4% is trans. Principal impurities are butynediol (specified as 2.0% maximum, typically less than 1%), butanediol, and the 4-hydroxybutyraldehyde acetal of butenediol. Moisture is specified at 0.75% maximum (Karl-Fischer titration). Technical-grade butenediol freezes at about 8°C. 

Herold, B., Rfeiffer, R, Radler, F. (1995) Determination of the three isomers of 2,3-butanediol formed by yeasts or lactic add bacteria during fermentation. Am. J. Enol Vitic., 46, 134—137. 

Problem 9.36 The ds and trans isomers of 2,3-dimethyloxirane both react with OH to give 2,3-butanediol. One stereoisomer gives a single achiral product, and one gives two chiral enantiomers. Which epoxide gives one product and which gives two ... 

While activation energies have been published for many isocyanate/ alcohol reactions, relatively few reports have been made of the heat of reaction. Bayer [136] reported a heat of reaction of 52 kcal mole , or 26 kcal equiv", for the hexamethylene diisocyanate/1,4-butanediol reaction. Lovering and Laidler [137] measured heats of reactions for the butyl alcohol isomers with several aromatic isocyanates. Values ranged from 18.5 to 25 kcal equiv . ... 

Polyhydric Alcohols.—Using a borate buffer at pH 9.2, Frahn and Mills have studied the zone-electrophoretic behavior of a number of diols (see Table VII). Thus 1,4-butanediol and 1,5-pentanediol were found not to react with borate ions, indicating that borate complexes involving 7- and 8-membered rings have little tendency to be formed. The more ready reaction of comparison with the erythro isomer, is not unexpected, since the 5-membered ring in the borate complex of the latter (but not the former) would possess eclipsed methyl groups at C2 and C3. The relative reactivity of the 2,3-butanediols toward borate... 

The same year, Gerlach described a synthesis of optically active 1 from (/ )- ,3-butanediol (7) (Scheme 1.2). The diastereomeric esters produced from (-) camphorsulfonyl chloride and racemic 1,3-butanediol were fractionally recrystallized and then hydrolized to afford enantiomerically pure 7. Tosylation of the primary alcohol, displacement with sodium iodide, and conversion to the phosphonium salt 8 proceeded in 58% yield. Methyl-8-oxo-octanoate (10), the ozonolysis product of the enol ether of cyclooctanone (9), was subjected to Wittig condensation with the dilithio anion of 8 to give 11 as a mixture of olefin isomers in 32% yield. The ratio, initially 68 32 (E-.Z), was easily enriched further to 83 17 (E Z) by photolysis in the presence of diphenyl disulfide. The synthesis was then completed by hydrolysis of the ester to the seco acid, conversion to the 2-thiopyridyl ester, and silver-mediated ring closure to afford 1 (70%). Gerlach s synthesis, while producing the optically active natural product, still did not address the problem posed by the olefin geometry. 

---