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The spectral changes that lithium perchlorate ions in ether solution impart upon various dipolar molecules have been explored at 25.0 O C . The molecules studied in this investigation all display UV-visible spectra, which are highly sensitive to solvent polarity (solvatochromism). Of the three types of molecules chosen for the present study, only N,N-dimethylindoaniline (phenol blue) displays UV-visible spectra that vary over the entire range of lithium perchlorate concentrations. For phenol blue, a change in the low-energy absorbance band of 104 nm is observed upon changing the solvent from pure diethyl ether to 5.05 M lithium perchlorate in ether. This corresponds to a stabilization of 8.01 kcal/mol for this transition. With the other indicator molecules, 2,6-diphenyl-4-(2,4,6-triphenyl-1 -pyridinio)phenolate (Reichardt's dye) and 8,9-diacylsesquifulvalenes, the lithium ion forms 1:l complexes. The exceptional sensitivity of Reichardt's dye to solvent polarity makes it an extremely discriminating probe for minute amounts of lithium ions in solution. An equilibrium expression was deduced that agrees well with the experimental data and leads to the following equilibrium constants for these molecules. The values for the Reichardt's dye are 5 X lo6 M-' in diethyl ether solutions and 1 X lo5 M-' in tetrahydrofuran solutions. The values for the 8,9-diacylsesquifulvalenes are 2. 39, 5.44,7.31, and 9.35 M-' for the dibenzoyl-, diformyl-, dicarbomthoxy-, and diacetyl-substituted compounds, respectively, in lithium perchlorate-tetrahydrofuran solutions and 15.8, 16.8, and 18.2 M-' for the dibenzoyl-, diformyl-, and diacetyl-substituted compounds, respectively, in lithium perchlorate-diethyl ether solution. The order of participation of lithium perchlorate in the equilibrium expression indicates that 1: 1 complexes are formed between dipolar molecules and lithium ions. Indeed, an order of 1 is displayed for all compounds, with the exception of 8,9-diacetyl-and 8,9-dibenzoylsesquifulvalene at low concentrations and 8,9-(dicarbomethoxy)sesquifulvalene at all concentrations of lithium perchlorate in diethyl ether, which form 2:l complexes with lithium ions. ( 8 ) Brooker, L. G. S.; Craig, A. C.; Heseltine, D. W.; Jenkins, P. W.; Lincoln, L. L.

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Spectral study of the cesium and lithium enolates of dibenzyl ketone (DBK) showed that both salts exist as contact ion pairs in THF solutions. The spectral data for the dicesium salt of DBK indicate that it exists as triple ions in which both cations are in contact with the dianion. The dilithium salt of DBK forms triple ions of two types in THF: in one, both cations are in contact with the DBK dianion, in the other, one of the lithium cations is solvent-separated. Evidence for dimerization of the ion pairs was obtained for both lithium and cesium enolates of DBK from UV-vis spectral (blue shift of the absorbance band at higher concentrations) and acidity (the decrease of pK at higher concentrations) studies. The dimerization constant for the cesium enolate of DBK obtained from the acidity data (3.5 x 10(3) M(-)(1)) is considered to be more accurate than that from the spectral analysis (1.7 x 10(3) M(-)(1)). The lithium enolate is much less dimerized than its cesium counterpart with a dimerization constant from acidity data of 4.2 x 10(2) M(-)(1). The first and second cesium pK values of DBK are 18.07 and 33.70, respectively, compared to the first lithium pK of 11.62.

Enantiopure 4-substituted oxazolidinones are well-known chiral auxiliaries for asymmetric synthesis of carboxylic acid derivatives. The 4-(phenylmethyl)-substituted oxazolidinones derived from D-or L-phenylalanine are known to be particularly useful. We have conducted chemical development studies toward an efficient and scaleable "one-pot" process for production of (S)-4-(phenylmethyl)-2-oxazolidinone 2. The first step in the process employed a sodium borohydride reduction of phenylalanine mediated by an additive. The second step utilized triphosgene as a phosgene source to effect cyclization of the intermediate amino alcohol. Both chemical steps and workup procedures were screened and optimized utilizing statistical design of experiments (DoE) and parallel synthesis. The procedure was further characterized in an automated reactor system that provided heat flow measurements and modeled production at the plant scale. The efficiency of this process was compared to those of others previously reported on the basis of raw material cost, time requirements, safety, and hazardous waste generation.