Product yields with temperature paper

In a 5-I. round-bottom flask (Pyrex) is placed a mixture of 500 g. of phthalic anhydride and 400 g. of 28 per cent ammonium hydroxide. The flask is fitted with an air condenser not less than 10 mm. in diameter and is then slowly heated with a free flame until the mixture is in a state of quiet fusion at a temperature of about 300°. It requires about one hour before all the water has gone and about one and a half to two hours before the temperature of the reaction mixture reaches 300° and the mixture is a homogeneous melt. It is advisable, during the heating, to shake the flask occasionally some material sublimes into the condenser and must be pushed down with a glass rod. The hot reaction mixture is now poured out into a crock, covered with a paper to prevent loss by sublimation, and allowed to cool. The product is practically pure without further treatment, and melts at 23 2-23 5 °. The yield is 470-480 g. (94-95 per cent of the theoretical amount). 

Take up the yellow solid residue in the minimum volume of dilute hydrochloric acid (0.1 mol dm"3, c. 25 mL). Transfer the solution to a separating funnel (250 mL) and add dichloromethane (30 mL). Separate the aqueous layer and wash it twice more with dichloromethane (2 x 30 mL). Raise the pH of the aqueous layer to 13 by adding potassium hydroxide pellets (test with pH papers). Extract the aqueous layer with chloroform (5 x 20 mL), combine the organic extracts and dry them over anhydrous potassium carbonate. Filter the mixture and remove the solvent on a rotary evaporator to yield a colourless solid which is dried under vacuum (0.1 mmHg) at room temperature (NB do not heat, to avoid sublimation). The product (2.71 g, 79%) is sufficiently pure to be used in this form, m.p. 113-114°C. 

The kinetics and mechanism of synthesis and decomposition of macrocyclic compounds are regarded as one of the most important aspects in the chemistry of these compounds. The majority of papers concern metal ions complexing with preliminarily synthesized macrocyclic ligands and metal ion substitutions by other metal ions in the preliminarily prepared complexes. Template synthesis, the most promising approach to the directed preparation of macrocyclic compounds with desired structures [17], plays a still more decisive role in the chemistry of macrobicyclic complexes with encapsulated metal ion. However, the literature contains only scarce data on the kinetics and the mechanism of the template synthesis of macrocyclic compounds because of the difficulties encountered in experimental determinations of kinetic and thermodynamic parameters, such as low product yields, nonaqueous media, high temperatures, and side reactions. 

A 11.46-g (30.00mmol) quantity of bis(l,2-ethanediamine)platinum(II) chloride (Alfa) is dissolved in a minimal amount of water in a SOO-mL Erlenmeyer flask. [The bis(l,2-ethanediamine)platinum(II) chloride must first have been carefully recrystallized twice to insure its purity. Recrystallization is best accomplished by dissolving the solid in SOmL of water, gravity filtering, and allowing the filtrate to evaporate slowly. Pure [Pt(en)2]Cl2 gives a colorless (not brown or yellow) solution when dissolved in water. Impure [Pt(en)2]Cl2 drastically lowers the yield of this procedure.] A 200-mL volume of concentrated HCl is added, and the solution is heated to 89 °C for 7 h. The solution must not be boiled. The reaction mixture is allowed to cool to room temperature, then it is chilled in an ice-water bath. The solid that forms is collected by vacuum filtration, and the filtrate is set aside for platinum recovery. The solid is then washed with lOOmL of water acidified with five drops of concentrated HCl. The product dissolves in this washing, and some insoluble yellow by-product, which is [Pt(en)Cl2], remains on the paper. This second filtrate is treated with 200 mL of concentrated HCl at room temperature, which precipitates the pure product. Yield 4.65 g (30%). 

Ikushima et al. studied the pressure and temperature effects on the stereoselectivity of ( )-Citronellol esterifrcation at the initial stage of reaction (up to 5.8% yield Scheme 4.9-4). Generally, the optical purity of the product decreased with increasing reaction rate and increasing yield. They found a spectacular temperature effect for the Candida cylindracea-catalyzed esterification. At constant pressure (84.1 bar) and constant yield (3.4-3.6%), a temperature decrease of only 4°C caused the optical purity (enantiomeric excess, ee%) to increase from a mere 4.1% to almost complete stereoselectivity, 98.9 % [59]. In later papers they report a strong but slighly less dramatic tern-... 

In a paper that described a detailed preparation of air-stable cinchona alkaloid-derived chiral quaternary ammonium phenoxides, the Mukaiyama group also used these to enantioselectively prepare 3,4-dihydropyran-2-ones 160 [85]. A low loading of organocatalyst 159 at low temperatures, in a series of solvents, resulted in the formation of the optically active lactone products in high yields with excellent control of enantio- and diastereoselectivity. This process was proposed to go through a phenoxide-ion-catalyzed domino Michael addition and lactonization catalytic cycle as illustrated below. Many variations of the ketene silyl acetals and a, -unsaturated ketones were combined in this domino process (Scheme 7.32). Earlier,... 

Add 25 g. of finely-powdered, dry acetanilide to 25 ml. of glacial acetic acid contained in a 500 ml. beaker introduce into the well-stirred mixture 92 g. (50 ml.) of concentrated sulphuric acid. The mixture becomes warm and a clear solution results. Surround the beaker with a freezing mixture of ice and salt, and stir the solution mechanically. Support a separatory funnel, containing a cold mixture of 15 -5 g. (11 ml.) of concentrated nitric acid and 12 -5 g. (7 ml.) of concentrated sulphuric acid, over the beaker. When the temperature of the solution falls to 0-2°, run in the acid mixture gradually while the temperature is maintained below 10°. After all the mixed acid has been added, remove the beaker from the freezing mixture, and allow it to stand at room temperature for 1 hour. Pour the reaction mixture on to 250 g. of crushed ice (or into 500 ml. of cold water), whereby the crude nitroacetanilide is at once precipitated. Allow to stand for 15 minutes, filter with suction on a Buchner funnel, wash it thoroughly with cold water until free from acids (test the wash water), and drain well. Recrystallise the pale yellow product from alcohol or methylated spirit (see Section IV,12 for experimental details), filter at the pump, wash with a httle cold alcohol, and dry in the air upon filter paper. [The yellow o-nitroacetanihde remains in the filtrate.] The yield of p-nitroacetanihde, a colourless crystalline sohd of m.p. 214°, is 20 g. 

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