Boiling-point determination report

Boiling point determination is less precise than that of melting points and conflicting boiling point data is not usually reported except when there appears to be a serious discrepancy between the different authors. 

A significant improvement in the conduction of this reaction was reported under microflow conditions in comparison with batch mode. Batch conditions involved a reaction time of 60 h at room temperature to afford the final product in a 62% yield. Under optimized microreactor conditions, the online HPLC-determined yield was 91 % in a 60 min reaction time (Scheme 2). Note that the microreactor setup allowed the reaction temperature to be higher than the atmospheric boiling point of the solvent. 

A, B, C The A, B, and C constants, except where given by the API reports, are calculated by means of the Thomson method [Chem. Revs. 38, 1-39 (1946)] using the determined boiling points at three different pressures. The three formulas for this are as follows ... 

Owing to decomposition, it is impossible to determine the precise boiling point, though Belayev and Yuzefovich [34] reported that at a pressure of SO mm Hg the boiling point of nitroglycerine is 180°C, whereas under a pressure of 2 mm Hg it is 125°C. 

Most of the earlier data on redistribution reactions or equilibria reported in the literature are of more or less qualitative character. One of the exceptions is the work of Calingaert (41-51) where in a series of papers entitled The Redistribution Reaction, the laws of probability were applied to a quantitative interpretation of the random redistribution of interchangeable substituents. In these studies, the respective redistribution products were determined quantitatively by fractional distillation of the equilibrated mixture. Although this method was fairly successful in the cases studied by Calingaert, there were many other systems to which it could not be applied due to too small boiling-point differences of the redistribution products or rapid rearrangement under the conditions of the distillation. 

Vapor pressures at ambient temperatures of a number of pesticides can be determined by using a du Pont 900 differential thermal analyzer to measure boiling points for a series of pressures down to 10 mm., or by using an effusion method for compounds having vapor pressures from 10 3 to 10 7 mm. Less than 100 mg. of the sample are required in either case. Accuracy can be determined by comparison with direct measurements available in the literature. Vapor pressures for phenoxy herbicide esters are lower than values reported in the literature. 

The student should report the temperature determined for each fixed point on both the Kelvin and Celsius scales. In cases where the temperature is a boiling point or sublimation point, calculate and report also the temperature on both scales corrected to a pressure of 1 atm. In the neighborhood of 1 atm, the boiling point of water increases with pressure by 0.037 K Torr. For liquid nitrogen, the increase is 0.013 K Torr. ... 

Quinoxalines are weakly basic the basicities of quinoxaline derivatives were determined potentiometrically and of 5,6-substituted 2,3-dimethylquinoxalines either spectrophotometri-cally, or by potentiometric titration. Quinoxaline has a melting point of 29-30 C, a boiling point of 108-111 °C/12 Torr, and 0.56 (— 5.52) quinoxaline 1-oxide has a pK of 0.25 and is, therefore, a weaker base than the parent compound.Ionization properties (e.g., ionization constants) show that quinoxaline is a relatively weak base. Quinoxaline has a dipole moment of 0.51 D in benzene." Polarographic studies were performed on quinoxalines," and electrochemical and spectroscopic characterization of, V,A -dialkylquinoxalinium salts has been reported. ... 

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