Water condensate extraction procedures

The layers were separated and four extractions with the light petroleum fraction (50-ml portions) were carried out without delay (note 1). The combined extracts were washed with ice-water and subsequently dried over magnesium sulfate. The solution was warmed in a water-pumpvacuum and the ethoxyacetylene condensed in a receiver cooled at -80°C (see Chapter I for the description of this procedure). Redistillation of the contents of the receiver at normal pressure (760 nmHg) through a 40-cm Vigreux column gave ethoxyacetylene, b.p. 52°C, n ° 1.3820 in 62-702 yield. 

Preparation of soil—sediment of water samples for herbicide analysis generally has consisted of solvent extraction of the sample, followed by cleanup of the extract through Uquid—Uquid or column chromatography, and finally, concentration through evaporation (285). This complex but necessary series of procedures is time-consuming and is responsible for the high cost of herbicide analyses. The advent of soUd-phase extraction techniques in which the sample is simultaneously cleaned up and concentrated has condensed these steps and thus gready simplified sample preparation (286). 

Medium Boiling Esters. Esterificatioa of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, eg, chloro- or bromoacetic, or pymvic, by the use of a third component such as bensene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. Bensene has been used as a co-solvent ia the preparatioa of methyl pymvate from pymvic acid (101). The preparatioa of ethyl lactate is described as an example of the general procedure (102). A mixture of 1 mol 80% lactic acid and 2.3 mol 95% ethyl alcohol is added to a volume of benzene equal to half that of the alcohol (ca 43 mL), and the resulting mixture is refluxed for several hours. When distilled, the overhead condensate separates iato layers. The lower layer is extracted to recover the benzene and alcohol, and the water is discarded. The upper layer is returned to the column for reflux. After all the water is removed from the reaction mixture, the excess of alcohol and benzene is removed by distillation, and the ester is fractionated to isolate the pure ester. 

A detailed procedure for the use of MCPBA recently appeared in Reagents for Organic Synthesis by Fieser and Fieser. The commercially available MCPBA (Aldrich) is 85% pure the contaminant, m-chlorobenzoic acid, can be removed by washing with a phosphate buffer of pH 7.5. The epoxidation is usually performed as follows a solution of 3 -acetoxy-5a-androst-16-ene (2.06 g, 6.53 mmoles) in 25 ml of chloroform (or methylene dichloride) is chilled to 0° in a flask fitted with a condenser and drierite tube and treated with a solution of commercial MCPBA (1.74 g, 20% excess) in 25 ml chloroform precooled to the same temperature. The mixture is stirred and allowed to warm to room temperature. After 23 hr (or until TLC shows reaction is complete) the solution is diluted with 100 ml chloroform and washed in sequence with 100 ml of 10% sodium sulfite or sodium iodide followed by sodium thiosulfate, 200 ml of 1 M sodium bicarbonate and 200 ml water. The chloroform extract is dried (MgS04) and evaporated in vacuo to a volume of ca. 10 ml. Addition of methanol (10 ml) followed by cooling of the mixture to —10° yields 0.8 gof 16a,17a-epoxide mp 109.5-110°. Additional product can be obtained by concentration of the mother liquor (total yield 80-90%). 

Weigh 40 g (dry soil weight) of the sample into a 500-mL round-bottom flask and add 200 irL of acetone-water (3 1, v/v). Reflux the sample at 80 °C for 1 h after attaching a condenser. After cooling the extract, add 5 g of Cellite to the flask, mix the contents well and filter the extract. Conduct the subsequent procedures in a similar manner as for rice grains and concentrate the filtrates to approximately 50 mL. 

Procedure. Pipette 5 ml nitrate-N standard solution into the distillation flask, add 1 drop octan-2-ol, approximately 0.5 g Devarda s alloy, 6 ml magnesium hydroxide suspension (or 0.5 g MgO), and steam-distil the ammonia into 5-ml boric acid solution in a 100-ml conical flask. After approximately 40 ml distillate has been collected over a 5-min period, wash the tip of the condenser into the distillate, add 2-3 drops mixed indicator solution and titrate with 0.005 M HjSO until the colour changes from green to purple. Carry out a blank distillation using 5 ml water instead of extract solution and subtract from the standard titration to give a difference of 5.0 ml. 

An alternative procedure is used by the submitter from this point to the final distillation of solvent and ester The condenser is then set for downward distillation, and about 40 ml. of alcohol is distilled. Then 100 ml. of water is added, and an additional 100 ml. of alcohol and water is distilled. The cooled residue is diluted with 200 ml. of water and the solution freed of insoluble organic material by washing three times with 50 ml. of ether. After acidification with 40 ml. of concentrated hydrochloric acid, the organic layer is extracted with three 50-ml. portions of ether. The combined ether extracts are washed with water and dried over anhydrous magnesium sulfate. 

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