Fisher Johns apparatus

Details of this standard ASTM method are given in Table 16.1. 

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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... 

The Fisher-Johns apparatus (Fig. 35) is different in that you don t use capillary tubes to hold the sample. Instead, you sandwich your sample be-... 

Kofler Micro Hot State Apparatus. Electrically heated apparatus which might be considered a modification and improvement of the Fisher-Johns apparatus. It permits microscopic studies of fusion, sublimation, crystallization and explosion phenomena Refs 1) L. Kofler, Mikrochemie 15, 242 (1934) 2) N.D. Cheronis J.P. Entrikin,... 

In order to determine the firing time of an expl, propint or pyro vs temp of heating, a few grains of sample are placed on die surface of preheated, and maintained at desired constant temperature, devices used for determination of melting point. One of such devices is Fisher-Johns Apparatus [described in Fisher Scientific Co, Pittsburgh ... 

The tin II product shows four peaks (from DSC data)-at 60, 85, 115 and 350 C. The tin IV product shows only two peaks at 85 and 370 C. The sodium ionomer shows peaks at 60, 95, 130 and beginning at 450 C. The pre-ionomer shows peaks at about 40, 90 and 430 C. In all cases, the highest transition appears to coincide with a loss in weight observed in the TGA and the lowest (approximately) corresponds to the softening temperature observed with the Fisher-Johns apparatus. It is believed that the lowest temperature corresponds to movement in the ethylene units and that the additional peaks may correspond to more complex movements involving the carboxylate moieties. 

Picrates. Melting points over 210° should not be taken of picrates in the usual liquid bath apparatus. Use a melting point bar such as the Dennis bar or a Fisher-Johns apparatus (Ref 88)... 

The product is scraped from the walls of the flask and broken up by means of a curved spatula. The solid is collected on a 12.5-cm. Buchner funnel, washed with two 150-ml. portions of dry ether, dried by suction on the filter for 5 minutes, and stored in a desiccator over sodium hydroxide and phosphorus pentoxide. Analytically pure 2-acetamido-3,4,6-tri-0-acetyl-2-deoxy-a-D-glucopyranosyl chloride is obtained weight 55-65 g. (67-79%) m.p. 127-128° (Fisher-Johns apparatus) (Note 7) typical — NHCOCH3 absorptions at 6.09 n and 6.49 n in the infrared. Evaporation of the mother liquors and addition of ether to the concentrated solution gives an additional 4-6 g. (5-7%) of crystalline product, m.p. 125-127°, that is sufficiently pure for most purposes. The pure product may be stored in an open dish in a desiccator at room temperature for at least 3 years without decomposition (Note 8). 

The Fisher-Johns apparatus (Fig. 50) is different in that you don t use capillary tubes to hold the sample. Instead, you sandwich your sample between two round microscope cover slides (thin windows of glass) on a heating block. This type of melting point apparatus is called a hot stage. It comes complete with spotlight. Look for the following. 

Iodoanisole (20 g, 85.5 mmol) was chlorinated in a chilled chloroform-ether mixture. Chilling with dry ice was necessary to precipitate the dichloride, which was air dried and weighed 15.7 g (51.6 mmol, 60%), m.p. 62-64°C. It was then hydrolyzed with 13 gNa2C03 and 35 mL 5 N NaOH, washed with water and acetone, and dried at 50°C under vacuum to afford 7.3 g 3-methoxyiodosobenzene (29.2 mmol, 52%). This compound was shaken in an amber jar for 40 h with 7 g iodoxybenzene, 1 L water and Ag20 freshly precipitated from 15 g AgNOs. After filtration and clarification of the resultant solution, addition of a KI solution yielded 5 g 3-methoxydiphenyliodonium iodide (11.4 mmol), in a yield of 39%, m.p. 176-177°C (Fisher-Johns apparatus, inserted at 100°C). 

If your melting point apparatus uses capillary tubes to determine the melting point, an evacuated sealed tube is necessary, since caffeine sublimes the melting point is above the sublimation temperature (see Chapter 4). The melting point may be obtained using the Fisher-Johns apparatus without this precaution. 

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