The Thomas-Hoover Apparatus

The Thomas-Hoover apparatus (Fig. 36) is the electromechanical equivalent of the Thiele tube or open beaker and hot oil methods (see Using the Thiele Tube ). It has lots of features, and you should look for the following. 

Light box. At the top of the device, towards the back, a box holds a fluorescent light bulb behind the thermometer. On the right side of this box are the fluorescent light switches. 

Fluorescent light switches. Two buttons. Press and hold the red button down for a bit to light the lamp press the black button to turn the lamp off. 

Thermometer. A special 300° thermometer in a metal jacket is immersed in the oil bath that s in the lower part of the apparatus. Two slots have been cut in the jacket to let light illuminate the thermometer scale from behind, and to let a thermometer periscope read the thermometer scale from the front. 

Thermometer periscope. In front of the thermometer, this periscope lets you read a small magnified section of the thermometer scale. By turning the small knob at the lower right of this assembly, you track the movement of the mercury thread, and an image of the thread and temperature scale appear in a stationary mirror just above the sample viewing area. 

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Sodium valproate does not melt, decompose, or physically change in the normal working range of the Thomas Hoover capillary melting point apparatus [5]. Valproic acid boils at 120-121 °C [2]. 

Except for the Thomas-Hoover and Mel-Temp apparatus, the capillary is held to the thermometer with a rubber band made by cutting a slice off the end of a piece of ra-in. rubber tubing. This rubber band must be above the level of the oil bath otherwise, it will break in the hot oil. Insertion of a fresh tube under the rubber band is facilitated by leaving the used tube in place. The sample should be close to and on a level with the center of the thermometer bulb. 

Melting points, measured in open capillary tubes using a Thomas-Hoover melting point apparatus, are uncorrected. Elemental analyses were performed by Galbraith Laboratories, Knoxville, Tennesee. % and 19C-NMR spectra were generally obtained with an IBM AF-100, if necessary the higher field Bruker WP-200 or AM-400 NMR spectrometer were employed. Chemical shifts are given in parts per million (ppm) on a a scale downfield from tetramethylsilane (TMS). Infrared spectra were recorded with a Perkln-Elmer 283 spectrophotometer. 

General. All NMR spectra were taken on a Bruker AMX-400 spectrometer in DMSO-dg with DMSO as a standard at 2.50 ppm. All NMR spectra were taken on the same machine at 100 MHz in DMSO-dg with DMSO as a standard at 39.50 ppm, unless otherwise noted. All melting points were taken on a Thomas-Hoover Uni-melt melting point apparatus. Reagents were used unpurified, and deionized water was used as the solvent. 

Determination of maxima in the mesophase-isotropic curves for each binary combination was made either by microscopical observation of a Kofler contact preparation of the pure components using a Thomas micro hot stage or by a technique described previously using a Thomas-Hoover melting point apparatus. 

All temperatures are uncorrected and are reported in degrees centigrade. Melting points were determined in open capillary tubes using a Thomas-Hoover melting point apparatus. Pressures are expressed as millimeters (mm) of mercury. Elemental analyses were performed at the University of Florida or Atlantic Microlabs, Inc. in Atlanta, Georgia. 

All boiling points and melting points are uncorrected. Capillary melting points were determined on a Thomas-Hoover melting point apparatus. Infrared were determined with perkin-Elmer Model 377 spectrophotometer. NMR spectra were obtained on a Varian T-60 spectrometer. Chemical shifts are reported on the 6 scale. Gel permeation chromatography measurements were performed using Altex pump, Sp 8200 UV detector and Styragel lO A, lO X columns. 

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