Corrections melting point

Corrected Melting-points. In all the above determinations of melting-points, the values obtained are described as uncorrected, since no allowance has been made for the fact that the column of mercury in the thermometer is at a lower temperature than that in the bulb. For most purposes it is sufficient to record this uncorrected value, which is usually only slightly lower than the corrected value. 

According to Prins the heptachloropropane can be isolated easily by pouring the reaction mixture into water and removing the unreacted materials by steam distillation. The process is stopped when the product begins to distil, and on cooling the residue is obtained as a colorless solid of the correct melting point. 

Archer, owing to very unfortunate coincidences, had mistaken acid potassium tartrate for the acetylamino acid. Goldfarb et al. prepared authentic 5-acetylamino-2-thiophenecarboxylic acid, mp 230 232°C (methyl ester, mp 171-171.5°C ethyl ester, mp 161°C), through reduction of 5-nitro-2-thiophenecarboxylic acid with Raney nickel in acetic anhydride and proved the structure by Raney nickel desulfurization to 8-aminovaleric acid. They also confirmed that the acid mp 272-273°C (methyl ester, mp 135-136°C ethyl ester, mp 116-117°C) is 4-acetylamino-2-thiophenecar boxy lie acid as originally stated by Steinkopf and Miiller. The statement of Tirouflet and Chane that the acid obtained upon reduction and acetylation of 5-nitro-2-thiophenecarboxylic acid melts at 272°C must result from some mistake as they give the correct melting point for the methyl ester. 

The corrected melting point is 209.5-210.0°. Melting points were obtained with a Fisher-Johns apparatus. The recrystallized sample retained a pale tan shade... 

Table 1 Corrected Melting Points of Compounds Suitable as Reference Materials in the Calibration of Thermometers...

Corrected melting points of compounds suitable as reference materials in the calibration of thermometers... 

In almost all samples of commercial anthranilic acid, even though showing the correct melting point, a small amount of insoluble material remains on diazotization. The clear liquor should be removed from this by decantation. 

Furancarboxylic acid (6, 44) is most satisfactorily purified by recrystallizing from carbon tetrachloride. A few cc. of water should be added to coagulate and float the dark impurities. The clear subjacent liquid is separated and deposits colorless crystals of correct melting point. 

The 2,4-dinitrotoluene used must be free from oil and have the correct melting point of 71°. 

Correction.—Melting points are usually given as uncorrected for correction the following formula is employed —... 

Some Corrected Melting Points for Standardising Thermometers.—... 

The melting points of pure samples of the following compounds are determined using a melting point bath or an electrically heated apparatus, in the manner detailed above. The correct melting points of the pure substances are given in parentheses. 

The sulfate on the filter was dissolved in 200 ml of hot water, the solution charcoaled hot, and the product precipitated from the clear colorless filtrate by the gradual addition of a solution of 20 grams of sodium hydroxide in 40 ml of water under chilling. The precipitate was filtered by suction and washed thoroughly with water on the filter. The white material, 17.5 grams (88%) showed the correct melting point of 200° to 201°C, according to US Patent 3,341,541. 

The base obtained in this way is a hard, yellowish white, crystalline mass with melting point between 80 and 90°C. One recrystallization from 500 cc. alcohol yields the pure base in nearly white, glistening crystals having the correct melting point of 91°. The yield of crude material is quantitative that of recrystallized base is over 90 per cent of the theoretical amount. 

Rintoul (2) has determined the correct melting-point for para mononitrotoluene. After much trouble in purification and separation from the accompanying ortho and meta forms, he finally determined the correct melting-point to be 51.6° C. and not 54° C. as was previously supposed. 

In some runs as many as five recrystallizations failed to furnish white crystals of the ammonium salt, but, in these runs, precipitation of the acid after three or four crystallizations gave a product having the correct melting point. 

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