Reflux gravity

After 12-24 hours of reflux the reaction is, for the most part, complete. The reaction mix will be a dark brown. So what does one do about all those brown particles and junk. Well, usually there aren t any. The solution should be uniformly dark. If any solids can be seen it means that they are insoluble in ethanol and can be removed from solution by gravity or vacuum filtration through a coffee filter or some paper towels. If it takes a day to drip through the filter then so-be-it. The ethanol with its payload of isosafrole will... 

Henderson and Sutherland have prepared a hydrocarbon synthetically which is possibly a modification of terpinene. They reduced thymo-hydroquinone, thus obtaining menthane-2-5-diol, which was heated for half an hour with twice its weight of sulphate of potash under a reflux condenser, and so yielded a terpene boiling at 179°, of specific gravity about 0 840 and refractive index 1-4779. 

To 10 c.c. of the oil (otto of rose or rose-geranium oil) 10 c.c. of formic acid 100 per cent, (specific gravity 1 22) is added, and the mixture gently boiled under a reflux condenser for one hour. The mixture is cooled, 100 c.c. of water added, and the whole transferred to a separator. The aqueous layer is rejected, and the oil washed with successive quantities of water as in the acetylation process. The formylated oil is dried with anhydrous sodium sulphate, and about 2 grams neutralised and saponified with alcoholic potash in the usual manner. The percentage of citronellol is then calculated from the following formula —... 

Pressure drop is only likely to be a major consideration in the design of vacuum condensers and where reflux is returned to a column by gravity flow from the condenser. 

Ancillary equipment attached to a tall vessel will subject the vessel to a bending moment if the centre of gravity of the equipment does not coincide with the centre line of the vessel (Figure 13.21). The moment produced by small fittings, such as ladders, pipes and manways, will be small and can be neglected. That produced by heavy equipment, such as reflux condensers and side platforms, can be significant and should be considered. The moment is given by ... 

A mixture of 118 g. (1 mole) of succinic acid, 188 g. (2 moles) of phenol, and 138 g. (83 ml., 0.9 mole) of phosphorus oxychloride (Note 1) is placed in a 2-1. round-bottomed flask fitted with an efficient reflux condenser capped with a calcium chloride tube (Notes 2 and 3). The mixture is heated on a steam bath in a hood (Note 3) for 1.25 hours, 500 ml. of benzene is added, and the refluxing is continued for an additional hour. The hot benzene solution is decanted from the red syrupy residue of phosphoric acid and filtered by gravity into a 1-1. Erlenmeyer flask. The syrupy residue is extracted with two 100-ml. portions of hot benzene, which are also filtered into the Erlenmeyer flask. The combined benzene solutions are concentrated to a volume of about 600 ml. (Note 4), and the pale yellow solution is allowed to cool, whereupon the diphenyl succinate separates as colorless crystals. It is filtered with suction on a Buchner funnel, washed with three 50-ml. portions of ether, and dried on a porous plate at 40°. The yield of diphenyl succinate, m.p. 120-121°, is 167— 181 g. (62-67%) (Note 5). 

A solution of 40 g. (0.2 mole) of sec-butyl 3-methylheptanoate in 100 ml. of ethanol containing 18.5 g. (0.3 mole) of potassium hydroxide and 20 ml. of water is heated under reflux for 30 minutes (Notes 7 and 8). The cooled solution is diluted with 200 ml. of water and acidified by the addition of 60 ml. of concentrated hydrochloric acid. The organic acid is extracted with three 100-ml. portions of 1 1 benzene-ether, and the combined benzene-ether extracts are washed with 50 ml. of saturated sodium chloride solution. The resulting solution is filtered by gravity through a bed of anhydrous magnesium sulfate. After removal of solvents by distillation, 26-27 g. (90-94%) of 3-methylheptanoic acid, b.p. 116-117710 mm., d 1.4242, is obtained by distillation in a modified Claisen flask (Note 9). 

B. Tetracycmoethylene. A mixture of 254 g. (0.25 mole) of the dibromomalononitrile-potassium bromide salt and 1 1. of dry benzene is placed in a 2-1. three-necked flask fitted with a sealed mechanical stirrer and a reflux condenser. The stirrer is started (Note 6), and 100 g. (1.57 g.-atoms) of precipitated copper powder (Note 7) is added. The mixture is heated at reflux with constant stirring for 10-16 hours. The benzene layer becomes progressively deeper yellow as the reaction proceeds. At the end of the reaction period, the hot mixture is filtered by gravity, using a fluted paper. Most of the heavy solid is easily retained in the flask and is heated under reflux with 300 ml. of dry benzene, with stirring, for 30 minutes. Filtration of the hot mixture is carried out as before. Two 25-ml. portions of hot benzene are used to wash the precipitate and are decanted through the filter. 

Trimethylene bromide prepared by direct distillation of the reaction mixture without the preliminary refluxing period contains appreciable amounts of trimethylene bromohydrin. In the purification of trimethylene bromide with sulfuric acid the high specific gravity of the former (1.987) must be borne in mind. Vigorous shaking with sulfuric acid may result in the formation of emulsions. 

Forget about Nat. Forget about the rat. Both stories are pure fiction. The truth is that the elevation of the reflux drum was 80 ft above the condenser. The specific gravity of the butane liquid was 0.59. This means that 80 ft of liquid exerted a head pressure of about 20 psig ... 

The reflux drum separates liquid and wet gas by gravity settling. A horizontal vapor-liquid separator works in much the same way as the vertical KO drum. 

Reflux 15 min at room temperature and filter through a Whatman no. 4 filter paper under gravity. 

B. 4-Metkyl-6-hydroxypyrimidine. To a hot solution of 10 g. (0.07 mole) of 2-thio-6-methyluracil in 200 ml. of distilled water and 20 ml. of concentrated aqueous ammonia in a 500-ml. round-bottomed flask is added 45 g. (wet paste) of Raney nickel catalyst (Note 3). About 30 ml. of distilled water is used to wash all the nickel catalyst into the reaction flask. The mixture is heated under reflux in a hood for about 1.5 hours. The catalyst is permitted to settle, and the clear solution is decanted and filtered by gravity. The catalyst is washed with two 75-ml. portions of hot water and is discarded (Note 4). The combined filtrate and washings (Note 5) are evaporated to dryness on a steam bath. The residue is placed in an oven at 70° to complete the drying process (Note 6). The yield of crude pyrimidine, m.p. 136-142°, is 7.0-7.2 g. (90-93%). 

Five grams of nickel(II) chloride 6-hydrate and 12.1 g. of tris(ethylenediamine)nickel(II) chloride 2-hydrate J are gently refluxed for 5 minutes with a mixture of 47.5 ml. of methanol and 2.5 ml. of water, shaking at first until all the salts are dissolved. A beautiful deep blue solution results. This is filtered by gravity while still warm into a 400-ml. beaker, and the flask and paper are washed once with 5 ml. of hot methanol. Seed crystals are obtained by adding 3 to 4 ml. of acetone slowly to 2 to 3 ml. of the blue solution and scratching or shaking until crystals form the separation of two liquid phases indicates the addition of too much acetone and makes the formation of crystals difficult. 

Fractional distillation works similarly. There is a division into vapor and liquid phases, the first enriched in solute(s) of relatively high vapor pressure and the second enriched in solutes of low vapor pressure. This enrichment is amplified by the relative displacement of phases. Again the relative motion occurs by virtue of the differences in densities of the phases coupled with the action of gravity. The downward flow (reflux) of the liquid stream is a direct consequence of gravity and is responsible for the accumulation of high-boiling components at the bottom of a distillation column. The motion of the vapor, countercurrent to the liquid stream, sweeps low boilers to the top [36]. 

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