INDUSTRIAL A N D ENGINEERING CHEMISTRY
820
Vol. 18. No. 8
New Reagent and Standard for Borax’ By LeRoy S. Weatherby and H. H. Chesny UNIVBRSITY OF SOUTHERN CALIFORNIA, LOS ANGELES, CALIF.
Inexpensive commercial gZucose (Cerelose) may be substituted f o r the expensive mannitol i n the titration method f o r the determination of borax. Borax may be titrated in alkali brine containing carbonates, bicarbonates, and neutral salts 6y making color standards. N T H E titration method for the determination of borax, boric acid is first liberated by a standard acid and the boric acid thus freed is then estimated by titration with a standard alkali. The titration of the weak boric acid can be made only in the presence of certain polyhydroxy compounds. The chief substances recommended for this purpose are mannitol, invert sugar, and glycerol. Mannitol is generally accepted as the standard. The possibility of estimating boric acid volumetrically has been known since 1893. Thompson2 was the first to make use of the fact that glycerol fortifies the weak boric acid. Boesecken and Van Rossen3 found that the electrical conductivity of boric acid is increased by the addition of certain organic compounds. Mellon and Morris4 examined a large number of such compounds, as mannitol, sorbitol, dulcitol, glycerol, erythriol, manna, xylose, rhamnose, mannose, fructose, invert sugar, polyphenols, glycolic and oxalic acids, and concluded that invert sugar is the most valuable substance of those examined from the viewpoint of cheapness, although they admit that mannitol is superior as to accuracy. Duncan6 studied the chemistry of the reaction of glycerol and boric acid and separated anhydrous glycerol boric acid to which he attributed the formula HC3H50HB03. Furthermore, he states that one equivalent of glycerol and two equivalents of boric acid form neutral sodium-glycerolborate, setting free boric acid and that further addition of glycerol develops acidity by forming with this liberated boric acid the more energetic glycerol boric acid. The new compound is not stable in the presence of water unless considerable glycerol is added. Angeno and Vallaa found that mannitol and boric acid unite in the ratio 1:1. They state that the electrolytic dissociation of the mannitol-boric acid is of the order of monobasic organic acids and is proportional to the concentration of the mannitol. Biltz and Marcus7 investigated the influence of magnesium chloride and calcium chloride on the titration of boric acid and concluded that even a strong excess of these salts does not interfere with the accuracy of the titration. The purpose of the present investigation was to compare the efficiency of the more commonly used reagents in the titration of boric acid, and t o test other similar compounds for the purpose of replacing these reagents with a less expensive and more easily obtained agent of q u a l accuracy. A further purpose was to establish conditions by which borax may be estimated accurately in brines, containing other alkali salts, as carbonates and bicarbonates.
I
Mannitol Glycerol Glucose Levulose Honey Invert sugar
All these compounds were tested as to purity and neutrality. A standard borax solution was made up from anhydrous C. P. sodium tetraborate, containing 18.9 grams per liter of solution. Procedure
The experiments were carried out by titrating 5-cc. samples of the standard solution with 0.1 N HC1 in the presence of methyl orange indicator to the dead neutral point. I n the cases where carbonates or bicarbonates were added to the standard borax solution, the mixture, after neutralization, was boiled for 3 minutes to expel all carbon dioxide. To the neutral solution one of the polyhydroxy compounds was added and then the mixture was titrated with 0.1 N NaOH in the presence of phenolphthalein. After the first pink color, indicating the end point of the reaction, was obtained, more of the polyhydroxy compound was added and the titration continued, until no more fading of the pink color occurred on further addition of the substance used. No less than three titrations were made in each analysis, with a n error of endpoint determination within 0.1 cc. from the mean. Titrations
(I) Pure borax solution (18.9 grams per liter): Pdiyhydroxy compound Mannitol Glycerol Glucose Levulose Honey Invert sugar
Received April 22,1926. 2 J . SOC.Chem. Ind., 19, 432 (1893). a Rec. trav. chin., 80,392 (1911). 4 THISJOURNAL, 16, 123 (1924). SPharm. J., 86, 104 (1911). Chem. Ztg., 36, 221 (1912). 2. anorg. Chem., 77, 131 (1912).
Borax found Grams/liter 18.9 19.1 18.9 19.9 22.2 20.1
( 2 ) Borax solution (18.9 grams per liter) in the presence of sodium carbonate (10.6 grams per liter): Polyhydroxy compound Mannitol Glycerol Glucose Levulose Honey Invert sugar
Borax found Grams/li t er 18.9 18.9 18.9 21.9 24.6 24.7
The same experiment was repeated using twice the amount of sodium carbonate: Polyhydroxy compound Mannitol G1ucose
Reagents
The following polyhydroxy compodds were used in the titrations:
Merck C. P. Pure deutral Comkercial Cerelose Levulose sirup, Merck, 33.3 per cent solution Boydens, clear, liquid Made by Gilmour’ss directions
Borax found Grams/liter 18.8 18.8
(3) Borax solution (18.9 grams per liter) in the presence of sodium chloride (50 grams per liter) : Polyhydroxy compound Mannitol Glycerol Glucose Levulose Honey Invert sugar
1
8
Analyst, 49, 576 (1924).
Borax found Grams/liter 18.9 19.0 18.9 22.1 23.5 22.1
I X D US TRIAL AND ENGINEERING CHEMISTRY
August, 1926
(4) Borax solution (18.9 grams per liter) in the presence of sodium sulfate (I50 grams per liter) and sodium carbonate (10.6 grams per liter): Polyhydroxy compound Mannitol Glucose
Borax found Grams/liter 18.9 18.8
( 5 ) Borax solution (18.9 grams per liter) in the presence of sodium carbonate (10.6 grams per liter), sodium bicarbonate (20 grams per liter), sodium chloride (150 grams per liter), and sodium sulfate (150 grams per liter) : Polyhydroxy compound Mannitol Glucose
Borax found Grams/liter 18.9 18.9
Amount of reagent necessary t o titrate 1.0 gram of anhydrous sodium tetraborate : Reagent Mannitol Glycerol Glucose Levulose Honey Invert sugar
Initially added 3 grams 10 cc. 30 grams 10 cc. 10 cc. 40 cc.
Totally added 5 grams 90 cc. 45 grams 10 cc. 10 cc. 80 cc.
In the case of levulose and honey the first end point obtained after adding initially 10 cc. of the agent was taken as final value, because these two compounds give end points which are dependent on the concentration of the levulose or honey present in the solution.
Titration in Presence of O t h e r S a l t s
When borax is titrated in the presence of other alkalies, as sodium carbonate or sodium bicarbonate, these mixtures do not show a definite end point when neutralized with 0.1 N HC1 against methyl orange indicator. Since the accuracy of the following alkali titration is dependent on the accuracy of the neutralization of the mixture, it was necessary to eliminate this source of error as far as possible. For this purpose the alkalinity of a certain amount of the borax solution and the alkalinity of certain amounts of the other salts were ti-
821
trated separately using 0.1 N hydrochloric acid with methyl orange as indicator. From the data thus obtained the total alkalinity of the mixture of borax with the other salts was calculated. The mixture was now titrated with 0.1 N hydrochloric acid and methyl orange indicator to the calculated end point. The color obtained by this titration was taken as a standard. For further experiments color charts were made, showing the exact color at the dead neutral point with varying concentrations of borax and carbonates. Conclusions
Borax, whether present alone or in mixture with other salts, may be determined accurately by using either mannitol or glucose. The largest difference was found in the presence of carbonate and sulfate, but even in this case it did not exceed the limits of the experimental error. Although it is possible to obtain fairly accurate results with levulose and honey, if they are added in proper concentration and the first change of color is taken as final end point, their use cannot be recommended since the results are dependent on the concentration of the added agent. The results obtained with glycerol and invert sugar are somewhat less satisfactory than those with mannitol and glucose. Though a larger quantity of glucose (about ten times) is required than of mannitol, this is no disadvantage, as a large background of white material is helpful in distinguishing the end point. As commercial glucose (Cerelose) may be obtained a t a cost of a few cents a pound, while the price of mannitol is around $6.50 a pound, the advantage of glucose may readily be seen. Commercial glucose in the pure form now obtainable is therefore recommended to replace mannitol in standard borax determination. The errors in the determination of borax in the presence of other salts are due to errors in the initial neutralization of the alkalinity, and not to the boric acid titration itself. This source of error may be eliminated by means of alkalinity tests and the establishment of color standards. ~
~
Estimation of the Unsaturated Content of Petroleum Products‘ By A. W. Francis AR’CHLR D. LITTLE,INC , CAMBRIDGE, MASS.
HE estimation of olefins in gasoline by means of sulfuric acid involves the uncertainty of the optimum concentration of acid which will remove the bulk of the olefins and practically none of the aromatics. There is also an error due to loss by vaporization, which may be considerable. Iodine and bromine have been used for this analysis, but neither has been quite satisfactory. The reaction with iodine is so slow that a large excess of iodine and a long reaction time must be used. The conditions of time and temperature have been standardized empirically, and probably merely attempt to balance the unreacted olefins against the substitution reaction in saturated compounds. With bromine there is still greater difficulty in avoiding substitution, and methods of correction have been employed, such as the measurement of the amount of hydrogen bromide evolved when a nonaqueous bromine solution is used, but these are cumbersome and unreliable. It is also difficult to keep the bromine solution of uniform strength, whether water or an organic solvent is used.
T
1
Received April 8 , 1928.
To overcome these difficulties, a method has been devised which employs a standard solution of potassium bromide and potassium bromate, which holds its strength indefinitely, and in acid solution generates bromine KBr03
+ 5KBr + 3HzS04-3KzSOa
f 3Hz0
+ 3Br~
the rate depending upon the strength of the acid. By making the solution only slightly acid the bromine can be generated slowly; and by vigorous agitation this is consumed by the double bonds fast enough to keep it a t very low concentration and thus avoid substitution reactions. This is important for reliable results. The fact that the gasoline does not mix with the reagent is no disadvantage, and may be desirable in avoiding substitution, but it does necessitate vigorous agitation. It makes no difference in the titration whether dibromides or bromohydrins are formed, as may be seen from the following equations: RCHBrCHBrR’
RCH=CHR’
+ Brz + HzO7
+ HzO
LRCHBrCHOHR’ f HBr Bromide and bromate have been used previously for es-
