Heating mantles, electric

If crystallisation commences as soon as the solvent cools or if large quantities of hot solution are to be filtered, the funnel (and fluted filter paper) should be warmed externally during the filtration (hot water funnel). Three types of hot water funnel are illustrated in Fig. 11,1, 6 no flames should be present whilst inflammable solvents are being filtered through the funnel of Fig. 11, 1, 6, a. Alternatively, the funnel may be surrounded by an electric heating mantle (see Section 11,57) the heat input may be controlled by a variable transformer. When dealing with considerable volumes of aqueous or other solutions which do not deposit crystals rapidly on cooling, a Buchner funnel may be used for filtration (see detailed account in Section 11,1 and Fig. 11 1, 7, c). The filter paper... 

For solids which melt above 100° and are stable at this temperature, drying may be carried out in a steam oven. The crystals from the Buchner funnel should then be placed on a clock glass or in an open dish. The substance may sometimes be dried in the Buchner funnel itself by utilising the device illustrated in Fig. 77, <33, 1. An ordinary Pyrex funnel is inverted over the Buchner funnel and the neck of the funnel heated by means of a broad flame (alternatively, the funnel may be heated by a closely-fltting electric heating mantle) if gentle suction is applied to the Alter flask, hot (or warm) air will pass over the crystalline solid. 

Place 3 3oz packets of Mildewcide into a 1L flask with an electric heating mantle and cork in the neck connected to a gas bubbler immersed in at least 550mL of distilled water. Heat the paraformaldehyde (what is in the Mildewcide) to between 180-200C (a temp, regulator is absolutely necessary for this step or use a silicone oil bath). The paraformaldehyde will depolymerize making formaldehyde gas in about 91% yield. Alternatively, the gas can be bubbled through the Ammonia solution directly (only for the brave ). If the Formaldehyde solution will not be used immedi-... 

In a 500-ml. round-bottomed flask fitted with a reflux condenser are placed 16.2 g. (0.08 mole) of dry a-naphthylthiourea (Note 1) and 180 ml. of redistilled chlorobenzene. The flask is heated at the reflux temperature by means of an electric heating mantle. Evolution of ammonia begins almost at once, and all of the solid dissolves after 30-45 minutes. The solution is maintained at reflux for 8 hours (Note 2) and then evaporated on a steam bath at water-pump pressure to remove all of the chlorobenzene. The residue crystallizes on cooling and is extracted with four 30-ml. portions of boUing hexane (Note 3). Removal of solvent from the combined hexane extracts affords pale yellow crystals of naphthyl isothiocyanate, m.p. 58-59°. The yield is 12.7-13.0 g. (86-88%). Recrystallization from hexane (9 ml. of hexane for 1 g. of solute) gives colorless needles, melting point unchanged (Note 4). 

Usually a small amount of material remains undissolved. This material does not affect the melting point significantly but can be removed if desired by forcing the solution, kept hot by an electric heating mantle, through the filter arrangement described above into a dry flask protected from moisture by a calcium chloride tube. 

The submitters used an electric heating mantle as a source of heat. 

B. l-Bromo-2-fluorobenzene. Cautionl This step should be carried outm a hood because the PFS evolved on thermal decomposition of the diazonium salt is poisonous. The apparatus consists of a 1-1., three-necked, round-bottomed flask equipped with a thermometer, a condenser, a magnetic stirrer (optional), and a 250-ml. Erlenmeyer flask that is attached by means of a short rubber Gooch connecting tube. The dry powdered hexafluorophosphate salt is placed in the Erlenmeyer flask, and 300 ml. of heavy mineral oil is placed in the round-bottomed flask. The mineral oil is heated to 165-170° by means of an oil bath or electric heating mantle and maintained at this temperature while the salt is added rapidly in portions over a period of 30 minutes. The flask is cooled rapidly to room temperature, the side flask is removed, and 400 ml. of 10% aqueous sodium carbonate is added slowly through the condenser. The mixture is steam-distilled until no more oil is visible in the distillate. 

This steam distillation removes ether, tetrahydrofuran, and other volatile neutral products. If too much water accumulates in the flask, it may be heated in an electric heating mantle after most of the ether has been removed. 

A 2-1. three-necked round-bottomed flask in an electric heating mantle is fitted with a mercury-sealed Hershberg stirrer, a dropping funnel, and an efficient reflux condenser topped with a tube containing soda lime and calcium chloride. In this flask are placed 21.3 g. (0.56 mole) of pulverized lithium aluminum hydride (Note 1) and 300 ml. of dry ether. The mixture is heated under reflux until most of the hydride has dissolved. A solution... 

A sand bath in an electric heating mantle was found to be satisfactory for the long-term heating process. 

The use of an electric heating mantle results in local overheating of the initially formed poly- or oligomeric products giving red, foul-smelling products instead. The product distills rather slowly (2-4 hr). 

Advancement reactions were performed using electric heating mantles. Temperatures of the resin, mantle/beaker interface, and mantle interior were recorded via thermocouples. Reaction mixtures were not protected from atmospheric oxygen. The advancement reaction was initiated at 120 C using O.IZ (weight/weight) triphenylphosphine. 

An electric heating mantle is then fitted under the flask, and the mixture is vigorously stirred and heated to reflux under nitrogen for 12-18 hours. After cooling to room temperature, a positive nitrogen pressure is maintained while the mechanical stirrer is replaced with a glass stopper. 

Our laboratory oxidations were carried out by bubbling dry air at 80 to 125 cc. per minute STP, at 110°C. through 500 ml. of olefin in a round-bottomed, 1-liter, standard-taper, three-necked flask equipped with magnetic stirrer, Therm-O-watch controller, electric heating mantle, and condenser. Alkenyl hydroperoxide numbers [Method I of Mair and Graupner (11)] and polymeric dialkyl peroxide numbers (Method III minus Method I of Ref. 11) were determined on small aliquots of about 5 ml. withdrawn at various times. 

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