Regeneration of the Walden Silver Reductor EUGENE
H. H U F F M A N , Radiation Laboratory,
University of
California, Berkeley, Calif.
When the reduction to chromous chloride is complete, as indicated by the blue color, the solution is poured into the reductor and allowed to percolate through the silver-silver chloride column. The solution is green for a while as it leaves the reductor. The reaction is complete when the solution comes out with a blue color. The chromous chloride solution is then rinsed from the reductor with 0.1 ill sulfuric acid and the reductor is ready for use.
T
HE usual method for regeneration of the silver reductor is
that given by the originators of the reductor (1). This method consists of filling the column with about 0.1 M sulfuric acid and allowing a zinc rod to remain in contact with the silver until the dark silver chloride has disappeared. Although effective, this method sometimes requires as much as 48 hours. \Then such reductors are subjected to considerable use, it may be necessary to have several of them undergoing reduction for each one in use. To avoid the necessity of having at least 12 reductors at hand, the following directions for regenerating the silver have been used in this laboratory:
The total time required for the regeneration of a reductor which has been darkened for three quarters of the length of the silver column is 20 to 30 minutes, including the preparation of the chromous chloride solution. The reductors have the same characteristics after this treatment as after regeneration by zinc.
Approximately 15 grams of crystalline chromic chloride are dissolved in 50 ml. of water in a 250-ml. Erlenmeyer flask and about 8 grams of granular zinc added. Concentrated hydrochloric acip is then added slowly until there is a brisk evolution of hydrogen, and more acid is added as the reaction subsides.
LITERATURE CITED
(1) Walden, Hammett, and Edmonds, J . Am. Chem. SOC.,56, 360
(1934).
N e w Type of Reflux Condenser W I L L A R D T. SOMERVILLE, Elmhurst, N. Y .
W
HEN a reflux condenser of conventional design is operated
Table 1.
a t or near its capacity, the friction between the ascending stream of vapor and the descending condensed film on the glass causes a reduction in the amount of return condensate and a holdup on the condensing surfaces. The condensed film is thickened and in a short time enough fluid is held back SO that the space between the condensing walls is bridged with liquid. This results in “slugging” or “flooding”, which becomes worse on the continued entrance of vapor into the condensing chamber. I t is then necessary to stop the operation to permit the fluid to drain back into the reaction vessel. Often it is not desirable or possible to interrupt the refluxing, especially when exothermic reactions are encountered. to allow the trapped condensate to return. The present, paper relates to a reflux condenser with increased capacity and a nonflooding feature.
...
The apparatus shown in Figure 1 (patent applied for) consists of a trap integrally constructed with an Allihn condenser; the upper part of the trap is cooled via the common wall. The trap has three or more openings in the floor, permitting the condensate to drain back t,o the reaction vessel. The path of the vapor, for the most part, is free of contact with returning condensate. When this apparatus is operated a t or near capacity, the retained liquid is held in the trap and does not impair the efficiency of the condenser. If any fluid is held in the bottom of the trap, it will return to the vessel when the violence of the ebullition subsides. This condenser has been found very useful in controlling bumping and foaming liquids, since they are thrown against the side wall and can drain back.
,
In Table I, data are given on an esterification using mineral acid as catalyst, and benzene as the azeotropic water-entraining substance. This reaction proceeded a t a rate faster than the water could be removed, resulting in the formation of numerous large
Esterification of Phenylacetic A c i d with n-Pentanol
(Reaction mixture, 15 moles of acid, 20 moles of alcohol, 500 ml. of benzene, 5 ml. of H I S O I ) Allihn Condenser of Same Condenser of Figure 1 Dimensions Water in Water in moisture trap Reaction water moisture trap Reaction water Time used collected used collected Min. Xl. % 411. % 0 0 0.0 0 0 0 15 35 12.4 32 10 8 25 48 17.0 42 14 9 45 96 33.9 84 29 8 55 124 44.8 108 38 3 151 70 53.3 131 46 4 214 90 75.6 186 66 9 259 105 91.5 229 81 3 27fja 135 97.4 268 95 0 150 282 e740 99.7 97 2 175 283 100.0 99 7 2.91 215 ... 282 100 0 0 Water measured was hot, which may account for larger volume. Theoretical amount is 270 rnl.
droplets of water in the reaction mixture. In a simultaneous experiment, a condenser constructed according to Figure 1 was compared with an Allihn condenser of the same dimensions, but without the trap. The reaction vessel was heated as strongly as possible wit’hout flooding the condenser. Table I indicates t,hat the time fan the completion of reactions of this type may be materially reduced by the use of this improved reflux condenser. The true differences between the tu-o condensers are greater than shown, owing to the reduction in reaction rate as the concentration of reactants are reduced. The last’ few milliliters of water are particularly slow in formation and removal. During this reaction, the condenser of Figure 1 was operated so that none of the condensate was held up in the trap; it could have been operated at a greater rate if some condensate had been held in this trap. The above data show that a condenser of this design has a larger capacity and can cope with bumping and foaming liquids. ACKNOWLEDGMENT
The cooperation of William Geyer in constructing several experimental models is appreciated. This condenser is available from the Scientific Glass Apparatus Co., Bloomfield, N. J.
Figure 1 278
