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Acetonitrile Recycling

Introduction

Acetonitrile is widely used in many synthetic reactions, and until recently, it was an easily-procured chemical.  However, since the end of 2007, Acetonitrile has been in increasingly short supply with a concomitant exponential increase in price. 

Acetonitrile wastes are of 2 types:  (1) Aqueous and aqueous-alcoholic wastes generally are obtained from HPLC synthetic procedures; and (2) anhydrous wastes generally are obtained from oligo-nucleotide synthetic procedures. 

Aqueous wastes generally contain anywhere from 20-70% Acetonitrile, 30-80% water, and small amounts of varying compounds like trichloroacetic acid or trifluoroacetic acid, peptides, fluorocein isothiocyanate, triethylamine, and peptide scavengers like thioanisole, ethanedithiol and phenol.

Anhydrous wastes generally contain around 70-80% Acetonitrile plus a variety of organic compounds, like dichloromethane, 1-methylimidazole, acetic anhydride, iodine, 2,6-Lutidine, trichloroacetic acid, pyridine and tetraethylthiuram disulfide.

Acetonitrile can be recycled easily from both anhydrous and aqueous wastes. The recovery of acetonitrile is virtually 100%, and the purity of the recovered acetonitrile is greater than 99.99% with an assay limit of less than 0.01%. Non-volatile contaminants are reduced by more than 10⁹ times.

Anhydrous wastes yield anhydrous acetonitrile, while aqueous wastes yield a concentrated acetonitrile-water mixture having a composition of approximately 80% acetonitrile and 20% water. Recoveries and purities are as noted above.

Anhydrous acetonitrile cannot be obtained directly from a water mixture because acetonitrile and water form an azeotrope. However, anhydrous acetonitrile can be easily prepared from a recycled acetonitrile-water mixture simply by using an anhydrous dehydrating agent such as calcium chloride, and then recycling the resulting anhydrous acetonitrile to remove any impurities.

When alcohol is present in an aqueous acetonitrile waste, recycling provides a highly purified mixture containing all of the acetonitrile, all of the alcohol, and a small amount of water. The composition of the recovered mixture will be different depending upon the initial amounts of the acetonitrile, alcohol and water that were present in the waste.