Drying agent magnesium sulfate

B. (E)-7,11-Dimethyl-6,10-dodecadien-2-yn-1-ol. To the suspension containing the acetylide intermediate 2, as prepared in part A, is added 14 g (460 mmol) of paraformaldehyde (Note 12) in portions (Note 13) over 10 min (Note 14). After stirrinj the mixture for 24 hr, the resulting suspension is poured into 450 mL of ice-cold watei (Note 15), the aqueous layer is saturated with sodium chloride, and the product is extracted with four 100-mL portions of ether. The combined organic extracts are dried over magnesium sulfate, the drying agent is removed by filtration, and the solvent is removed at room temperature on a rotary evaporator. The residue is distilled through a short-path distillation apparatus to provide a forerun of 2-butyn-1 -ol (bp 42-46°C, 6 mm), followed by 10.5 g (68% yield) of (E)-7,11 -dimethyl-6,10-dodecadien-2-yn-1-ol as a colorless liquid, bp 120-124°C (0.5 mm) (Note 16). 

Undecanedione (92.1 g, 0.5 mol) is added to a solution of 16.0 g (0.4 mol) of sodium hydroxide in 800 mL of water and 200 mL of ethanol in a 2000-mL round-bottomed flask. The mixture is refluxed for 6 hr, cooled to room temperature, and extracted with ether. The combined ether phases are dried with magnesium sulfate, and the solution is separated from the drying agent and concentrated at room temperature under reduced pressure. The residual oil is distilled through a 30-cm Vigreux column. The pure compound boils at 65-67°C/0.5 mm and weighs 70-73 g (84-88% based on the diketone) (Note 8). 

To 21.6 kg (17.8 I) of 98% formic acid was added 1.14 kg (7.5 mols) of D-(-)-mandelic acid and the reaction mixture was heated for 4 hours at 70°C with stirring. The excess formic acid was evaporated off in vacuo and the residual syrup was dissolved in 6 I of benzene. The solution was washed twice with 6 I portions of water and was dried over magnesium sulfate. The drying agent was filtered and washed with 1.5 I of benzene, the washes being added to the filtrate. The dried filtrate was evaporated in vacuo to obtain the D-(-)-mandelic acid formate ether as a syrup. The product can be crystallized from cyclohexane to yield material melting at about 55°C to 58°C. 

Alkyl Chlorides. 3-Chloropentane was prepared by the reaction of thionyl chloride with 3-pentanol. Hexamethyl-phosphoric triamide, HMPT, was used as a complexing agent to ensure substitution at the 3 position (17). The organic layer was dried with magnesium sulfate and distilled. The middle fraction, b.p. 104°C, was collected for use. 1-Chloropentane was purified by repeated distillations. The above preparation procedures ensure maximum purity of the compounds for ESR study. 

The preceding method removes water, ethanol, and acetic acid. Drying over calcium chloride is not recommended. Ethyl acetate containing abnormal amounts of ethanol should be shaken with saturated sodium chloride solution and dried over magnesium sulfate before being treated with acetic anhydride.35 The ester can be dried by phosphoric oxide if it is decanted from the drying agent before distillation. 

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