Acetone dicarbonic acid

The original Garner preparation3 of 5 involves the conversion of serine into the protected methyl ester 3 and controlled reduction of the latter by DIBAL. The reaction sequence employed for the preparation of 3 involves the protection of the amino acid as N-Boc derivative using di-tert-butyl dicarbonate, esterification with methyl iodide or diazomethane, and acetonization with 2,2-dimethoxypropane under acid catalysis. The N-Boc methyl serinate and the ester 3 require purification by vacuum distillation or chromatography. In a modification to this procedure reported by McKillop,2 the esterification reaction of serine is carried out first by methanol/acetyl chloride. The resulting ester is then converted into the N-Boc derivative 2 with di-tert-butyl dicarbonate and the latter transformed into 3 by acetonization. This procedure avoids... 

Procedure Transfer about 2 g of sample, accurately weighed, into a 250-mL beaker, and dissolve it in 100 mL of acetone. Add 25 mL of 1 N Di-n-butylamine by pipet, allow the mixture to stand for 5 min, and titrate with 1 N hydrochloric acid, determining the endpoint potentiomet-rically. Perform a blank titration (see General Provisions), and make any necessary correction. Calculate the percent Dimethyl Dicarbonate in the sample taken by the formula... 

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