Yellowing reaction

Place 32 g. of potassium ethyl xanthate (Section 111,166) and 50 ml. of absolute ethyl alcohol in a 500 ml. round-bottomed flask provided with a double surface condenser. Add 32 g. (16-5 ml.) of ethyl iodide. No reaction appears to take place in the cold. Heat on a water bath for 3 hours a reaction sets in within 15 minutes and the yellow reaction mixture becomes white owing to the separation of potassium iodide. Add about 150 ml. of water, separate the lower layer, and wash it with water. Dry it with anhydrous calcium chloride or anhydrous calcium sulphate and distil from a 50 ml. Claisen flask. Collect the ethyl S-ethyl xanthate at 196-198°. The yield is 23 g. 

Nitrosomethylurea. Acetamide method. To a solution of 59 g. of acetamide in 88 g. (28 ml.) of bromine (1) in a 4-litre beaker add dropwise, with hand stining, a solution of 40 g. of sodium hydroxide in 160 ml. of water. Heat the resulting yellow reaction mixture on a steam bath until eflfervescence sets in (2), after which continue the heating for 2-3 minutes. CrystaUisation of the product from the yellow or red coloured solution usually commences immediately. Cool in an ice bath for 1-2 hours, collect the product by suction filtration, wash with a little ice-cold water, and dry in the air. The yield of colourless acetylmethylurea, m.p. 178-180°, is 50 g. 

Uric acid 2,6-Dichloroquinone- Yellow reaction 4-chloroimide product... 

The two most common enzyme labels for secondary antibodies are alkaline phosphatase (AP) used in conjunction with the substrate p-nitrophenyl phosphate, which results in a yellow reaction product, and horseradish peroxidase (HRP) used in conjunction with the substrate ABTS and H2O2, which results in blue-green reaction product see Chapter 23). 

The addition of bromine to quaternary ammonium bromides to provide the tribromides is most easily achieved in a reaction column with the solid while a stream of air carries the required amount of bromine (Scheme 11). Thus, in the case of tetrabutylammonium bromide (TBAB), a sharp yellow reaction front is obtained while bromine is quantitatively added and the pure bromi-nation agent TBABrg is obtained. Small runs can be quantitatively performed with 0.5 bar bromine vapor and the unground crystals of TBAB [28]. Equally simple is the gas-solid addition of chlorine to triphenylphosphane to give triphenylphosphane dichloride [28]. 

A. Ethyl 3-iodoproplonate. A 1-L, round-bottomed flask equipped with a magnetic stirring bar and a reflux condenser is charged with ethyl 3-chloropropionate (27.3 g, 0.2 mol) (Note 1) and acetone (400 mL). Sodium iodide (300 g, 2 mol) (Note 2) is added to the dear solution and the mixture is refluxed for 16 hr. The resulting pale yellow reaction mixture is cooled to room temperature, the stirring bar and reflux condenser are removed and the acetone is removed on a rotary evaporator at AO C/SSO mbar (412 mm). The residue is taken up in diethyl ether (300 mL) and washed with a saturated aqueous solution of sodium... 

A MiXTbire of 12 g. (0.50 gram atom) of magnesium turnings, 130 g. (1.0 mole) of ethyl acetoacetate, 200 g. of benzene (dried over sodium), and 120 g. (1.50 moles) of acetyl chloride is heated under reflux for two hours in a i-l. round-bottomed flask provided with a condenser closed by a calcium chloride tube and supported in an oil bath (85-90°) (Note 1). The yellow reaction mixture is cooled in an ice bath, and the liquid portion decanted into a separatory funnel. The residue in the flask is washed twice with 50-cc. portions of ether, and the ethereal solution poured over ice. The ether-water mixture is then added to the benzene solution in the separatory funnel, and the mixture is shaken thoroughly (Note 2) the aqueous layer is drawn off and discarded. The benzene-ether solution is washed once with 500 cc. of 5 per cent sodium bicarbonate solution, once with 50 cc. of water, and finally dried over calcium chloride. The ether and most of the benzene are removed by distillation from a water bath, and the remainder of the benzene is driven off at 50°/5o mm. The ethyl diacetylacetate is then precipitated from the residue as copper derivative by the addition of 1200 cc. of a saturated aqueous solution of copper acetate (Note 3). After addition of the copper acetate solution, the contents of the flask are shaken vigorously now and then and allowed to stand for an hour to ensure complete precipitation of the copper derivative. The blue copper derivative is filtered on a Buchner funnel, washed with two 50-cc. portions of water, and transferred directly to a separatory funnel where it is mixed with 600 cc. of ether. 

Preparation of the Pentafluorophenylthionocarbonate 46 The disaccharide 45 [Eq. (19)] (0.1 mmol) was diluted with 1 mL of dry toluene, and (V-hydroxysuccinimide (0.1 mmol) was added. Pentafluorophenyl chlorothionoformate (0.12 mmol) was then added dropwise, and finally anhydrous pyridine (0.5 mmol) was added. The yellow reaction mixture was heated to 80°C until TLC indicated that the reaction was complete. The product was purified by placing the entire reaction mixture on a 2 x 16-cm bed of silica gel and eluting with 4 1 petroleum ether-diethyl ether to give 0-(3,4,6-tri-C>-beiizyl-2-0-[(pentafluorophenoxy)thiocarbonyl]-P-D-glucosyl)-(l— 6)-l,2 3,4-di-0-isopropylidene-a-D-galactopyranose 46 in 77% yield and as a colorless oil [a]D —53.8° (c 0.40, CHClj). 

A well-stirred solution of 0.09 g l-(2,5-dimethoxy-4-(2-hydroxy-ethyl)phenyl)-2-(2,2,2-trifluoroacetamido)propane in 15 mL CH,C12 was cooled to -78 °C and treated with 0.05 g diethylaminosulfur trifluoride (DAST) added dropwise. The pale yellow reaction solution was stirred an additional 5 min and then brought up to room temperature and stirred for 1 h. There was then added (cautiously) 3 mL H20 followed by additional CH2C12. The phases were separated, the organic phase washed with H20, dried with anhydrous Na.SO, and, after filtering off the drying agent, stripped of solvent under vacuum. There was thus obtained 0.088 g of l-[2,5-dimethoxy-4-(2-fluoroethyl)phenyl]-2-(2,2,2-trifluoro-acetamido)propane as a white solid with a mp of 102-104 °C. 

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