Diazomethane standardized solution

Diazomethane In a distillation flask equipped with an distillation funnel and a cooler, place a solution of 5 g of potassium hydroxide in 8mL of water and 25 mL of ethanol. Warm the distillation flask to 65 °C in a water-bath. Add a solution of 21.5g (0.1 mol) of A-methyl-lV-nitroso-p-toluenesulfamide in 130 mL of diethyl ether through the instillation funnel in 5 min. If the distillation funnel becomes empty, pour 20 mL of diethyl ether into the funnel, and distill it gradually. Continue distillation until the distilled ether solution becomes colorless. About 3 g of diazomethane is contained in the whole resultant ether distillate. Caution these procedures should be conducted in a laboratory hood Orbencarb, methyl 2-chlorobenzylsulfone (I), 2-chlorobenzoic acid (II), methyl 2-chlorobenzoate analytical standard materials (Ihara Chemical Industries Co., Ltd) Orbencarb and I standard solution for gas chromatography 1.0 qgmL in acetone Methyl 2-chlorobenzoate standard solution for gas chromatography 0.1 qgmL" in n-hexane... 

Prior to extraction, water samples were filtered through precleaned Whatman GF/F filters (using pure acetone/n-hexane) in order to remove suspended particulate matter from the aqueous phase. A sequential liquid/liquid extraction procedure was applied to approximately 1000-mL aliquots of the water samples using the solvents n-pentane, dichloromethane and dichloromethane after acidification to pFl 2. Each extraction step was carried out in a separating funnel with 50 mL of the solvent. The third extraction was applied to the pre-extracted water samples after addition of 2 mL of concentrated hydrochloric acid that was pre-cleaned by intense extraction with n-hexane. Subsequently the organic layers were separately dried by filtration over 1 g of anhydrous granulated sodium sulphate (Merck, Darmstadt, FRG) and 50 pL of an internal standard solution containing routinely d34- -hexadecane (6.0 ng/pL), dio-anthracene (5.1 ng/pL) and di2-chrysene (4.7 ng/pL) in n-hexane was added. Acidic compounds in the third extract were methylated by addition of a diazomethan solution and subsequent reconcentration. Prior to GC/MS analyses the extracts were reduced to a final volume of approximately 25 pL by rotary evaporation at room temperature. 

To determine the exact diazomethane content, allow an aliquot portion of the ethereal diazomethane solution to react with an accurately weighed amount (say, about 1 g.) of A. R. benzoic acid in 60 ml. of anhydrous ether. The solution should be completely decolourised, thus showing that the benzoic acid is present in excess. Dilute the solution with water and titrate the excess of benzoic acid with standard 0 IN alkali using phenolphthalein as indicator. 

An alcohol-free solution of diazomethane in ether is prepared as in Chapter 17, Section III. This solution is approximately 0.5 M in diazomethane and may be standardized by titration as follows benzoic acid (0.6 g, approx. 0.005 mole) is weighed accurately into an Erlenmeyer flask and suspended in 5 ml of ether. The diazomethane solution (approx. 5 ml) is added from a buret with swirling, care being taken that an excess of unreacted benzoic acid remains (the yellow color of the diazomethane should be completely discharged). The excess benzoic acid is now titrated with standard 0.2 N sodium hydroxide solution, and the concentration of diazomethane is calculated. 

An etherial solution of diazomethane is added to the benzene extract to form the methyl ester of the chlorophenols. After about lh, the solution is evaporated to the original volume. The extract is injected into the gas chromatograph and the result compared with a standard treated the same way. 

A solution of diazomethane (CHjNj) in ether was prepared and added (excess) in drops of the solutions of extracts, EF-1 and standard (Img) CHCI3 or MeOH. The resulting solutions were allowed to stand for 12 hours and the ether removed by passing a stream of N2 [Leonard, Lygo, Procter, 1995]. 

PREPARATION OF THE METHYL ESTER—TRIMETHYLSILYL ETHER. The standard acid (0.5 mg) or the residue obtained from the urine extraction was dissolved in 0.5 cm3 of methanol. Ethereal diazomethane (1 cm3) was then added and allowed to stand for 1 min. Ethereal diazomethane was prepared by the reaction of p-tolylsulphonyl-methyl nitrosamide with an alcoholic solution of KOH. 

The submitters used an undistilled ethereal solution of diazomethane, prepared from nitrosomethylurea (Note l).3 For use in the hydrogen-deuterium exchange reaction described, ethereal diazomethane solutions prepared by any standard preparative procedures (Note I)2-3,5 appear to be equally satisfactory. 

The concentration of diazomethane may be determined by reaction of an aliquot of the ethereal solution with a weighed excess of benzoic acid in cold (0°) ether solution as described in an earlier volume of this series.3 The unchanged benzoic acid is then determined by titration with standard aqueous 0.1 M potassium hydroxide. 

A sample (ca. 1 g) of K-crotonate was placed in a Pyrex tube (6 mm i.d. (x200 mm) and heated in a metal bath maintained at a constant temperature. The tube was evacuated through the reaction. After a given time the reaction tube was taken out of the bath and allowed to cool to room temperature. The heat-treated salt was weighed and dissolved in aqueous hydrochloric acid solution and extracted with ether. The ether extract was treated with diazomethane. The methyl ester derivatives of the products were subjected to analysis by gas chromatography using diethyl maleate as internal standard. 

Diazomethane is prepared from nitrosomethylurea8 by the method of Bachmann and Struve. The yield of diazomethane is determined by treatment of a 10-ml. aliquot of its ethereal solution with a solution of an excess of benzoic acid in ether, followed by titration of the excess acid with a standard alcoholic solution of potassium hydroxide. Then the diazomethane solutions are dried over pellets of potassium hydroxide at —50°. 

The conversion was quantitative (>95%). The methanolic solution was cooled and neutralized with a small excess of sodium carbonate. Acetals were extracted from methanol with light petroleum. For structural studies, acetals were oxidized to the corresponding acids by the action of chromic oxide in glacial acetic acid. The esters produced by the esterification with methanolic HC1 were chromatographed and compared with standards. Schogt et al. [66] used silver oxide for the oxidation and diazomethane for the esterification. 

Pyromellitic acid tetramethyl ester, mp 142-143 °C, prepared by diazomethane methylation of pyromellitic acid, is used as the internal standard and is stored as a dichloromethane solution (—1 mg/ml) in a freezer. (Any loss of solvent from the solution is conveniently verified by weighing.) From this solution, the exact volume corresponding to from 200 to 1000 pg of the internal standard is withdrawn and added to the ester mixture to be analyzed. The amount of internal standard chosen is dependent on the amount and type of sample. For samples where a high yield of esters is expected, the upper level of internal standard is used. 

Standards of the methyl esters of 2-methyl-4-chlorophenoxy acetic acid (MCP), 2,4-D acid, and 2,4,5-T acid were made by preparing dilute solutions of each of the acids in 3% NaHC03 and treating suitable aliquots with diazomethane as described in the analytical procedure steps 3-8 below. A final standard concentration of 0.5, 2.0, 30 nanograms per microliter for 2,4,5-T, 2,4-D and MCP, respectively, was suitable. Standards containing a 1 1 mixture of isopropyl and butyl 2,4-D and a 25 2 1 mixture of methyl MCP, methyl 2,4-D, and methyl 2,4,5-T were prepared to simplify sample analysis by standard addition. 

Add an aliquot of diazomethane solution to an accurately weighed, excess quantity of benzoic acid in ether. Dilute the mixture with ether and titrate with a standard alkali solution to calculate the quantity of acid remaining. 

Procedures (i) Esterification by diazomethane. Mix 1 ml of an ethereal indole acid standard (1 mg/ml) with 3 ml of an ethereal-diazomethane solution. CAUTION Diazomethane is explosive and poisonous. After... 

To extend this strategy to MIPs a well-studied MIP system was used to generate the racemic MIP starting material [12,15,16]. Racemic PAA was imprinted in the standard MAA/EGDMA matrix. This racemic MIP was equilibrated with enantiomerically pure L-PAA and then treated with diazomethane. Esterification presumably reacts with the unprotected D-selective sites. Verification of the enantioselectivity in the modified polymer was carried out using batch rebinding studies (Scheme 10). The polymer was equilibrated with racemic PAA. The observation of enantiomeric excess in the free solution confirms the enantioselectivity of the modified polymer. 

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