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Purification of Laboratory Chemicals, 8th Edition by W.L.F. Armarego

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L-Isovaline (2-amino-2-methylbutyric acid) [595-40-4] C5H11NO2, M 117.2, m ca 300° (sublimes in vac), [α]D25 + 113.1 (c 5, H2O), [α]D25 + 10 (5M HCl), pKEst(1) ~2.4, pKEst(2) ~9.7. Crystallise it from aqueous Me2CO, or better dissolve in H2O and add excess Me2CO. [Baker et al. J Am Chem Soc 74 4701 1952, DOI: 10.1021/ja01138a502; Greenstein & Winitz The Chemistry of the Amino Acids J. Wiley, Vol 3 p 2573-2577 1961.]

L(S)-Leucine [61-90-5] C6H13NO2, M 131.2, m 293-295°(dec), [α]D25 + 15.6 (5M HCl), pK125 2.33, pK225 9.74. Likely impurities are isoleucine, valine, and methionine. Crystallise L-leucine from water by adding 4 volumes of EtOH. It sublimes at 180-188°/0.3mm with 99.1% recovery, and unracemised [Gross & Gradsky J Am Chem Soc 77 1678 ...

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