Saponification Method for Roslin Esters ALBERT E. JOHNSON and R A Y V. LAWREIJCE Naval Stores Station,
U. S. Department o f Agriculi ire, Olurtee, Fla.
The saponification time of rosin esters is reduced b? 1 he use of hydrazine. Dark grades of rosin are bleached by the hydrazine, so that a phenolphthalein end poinl. is easily seen. Good reproducibility and agreement v ith theoretical values were obtained using a saponification time of 1 hour.
Table I.
Sap. No. Xiethyl dehydroabietate, m.p. 62.568.5' C . ( 6 ) ,theor. sap. N o . = 178.4 -4.v.
177.8 178.4 179.0 178.0 178.3
Av.
184.9 184.3 184.9 184.5 184.5
Lactone of hydroxytearahydroabietic acid, m.p. 130.5-131.5° C. (71, theor. sap. N o . = 184 6
T
HE increased use of complex esters of rosin has made it necessary to develop a simple and accurate saponification
method suitable for routine use. Most procedures for the saponification of rosin esters (1-6) require special care to avoid formation of dark solutions that are difficult to titrate. Some saponification solutions are viscous and difficult to pipet accurately. The method described involves the use of a small amount of hydrazine in the solution used for saponification. Its presence aids in the saponification and it also acts as a decolorizing agent for many of the color bodies commonly found in rosin esters.
KJ\- gum rosin
181.1 180.8 181.0 181.3 Ar.
REAGENTS
Hydrochloric Acid Solution (0.25 to 0.50N), accurately standardized. n-Hexyl Alcohol-Potassium Hydroxide Solution. Dissolve 40 grams of reagent grade potassium hydroxide and 20 ml. of 85% hydrazine hydrate in 1 liter of n-hexyl alcohol. Allow this solution to stand 24 hours and then filter t o remove any insoluble matter. The n-hexyl alcohol used to prepare this solution should be redistilled ffom potassium hydroxide, over q-hich it has been etanding overnight, or with which it has been refluxed for 1 hour. Phenolphthalein Solution. Dissolve 1 gram of phenolphthalein in 100 ml. of 95y0 alcohol. and neutralize the slightly acid alcoholic solution with sodium hydroxide solution.
Saponification of Rosin Estersa
181.O
S wood rosin
173.1 173.4
Glycerol ester of rosin
168.8 168.0
Pentaerythritol ester of g u m rosin
149.0 150.0
XIaleic modified glycerol ester of rosin
233.2 233.4 132.9 133.2
Phenol formaldehyde-modified glycerol ester of rosin a . 1.000-gram sample, 25 mi. of 0.5N potassium hydroxide solution i n nhexyl alcohol containing 20 mi. of 85% hydrazine hydrate per liter, refluxed gently for 1 hour.
9 d d 50 nil. of neutral ethyl alcohol, or reagent grade isopropy alcohol, and titrate with the standard hydrochloric acid solution, using 1 ml. of the phenolphthalein solution. Conduct a blank determination on 25 ml. of the hexyl alcoholpotassium hydroxide solution, using the same pipet and draining for the same length of time.
PROCEDURE
IYeigh 1.00 i 0.001 gram of the sample of rosin ester into a 250-ml. alkali-resistant saponification flask. Pipet 25 ml. of the hexyl alcohol-potassium hydroxide solution, allowing the pipet t o drain for a definite time. .4dd a few particles of silicon carbide boiling promoters. Connect the flask preferably to a water condenser or to an air condenser made from glass tubing, 15-mm. inside diameter, having a minimum length of 32 inches. Place on a hot plate and boil the solution gently for a t least 1 hour. Remove the condenser and cool t o room temperature.
I
,
/-
RESULTS
When saponified for 1 hour by the foregoing procedure, purified methyl dehydroabietate, melting point 62.5-63.5' C. (61, was found to have a saponification number of 178.3. Theoretical value is 178.4. This value was duplicated within 1 0 . 7 unit. Upon acidification of the saponified solution of this ester, the dehydroabietic acid precipitated readily and after one crystallization from hot ethyl alcohol it had a melting point of 167" to 170" C. (6). Samples of the lactone of hydroxl tetrahydroabietic acid, melting point 130.5-131.5' C. ( 7 ) ,gave saponification numbers of 184.9 to 184.3, after refluxing for 1 hour. Theoretical for this lactone is 184.6. The hydroxytetrahydrobietic acid which precipitated upon acidifying the saponification solution had a melting point of 155" to 160" C. ( 7 ) . The results obtained with eeveral rosin esters are 1iPted in Table I. DISCUSSIOY
a Q
'T
50
I
0
I
N O R M A L I T Y OF
Figure 1.
.2
KOH,
.3 HEXANOL
J
4
5
SOLUTION
Effect of hydrazine on alkali saponification of rosin esters
1.000 g r a m of m e t h y l dehydroahietate in 25 ml. of reagent
The hydrazine-heuyl alcohol saponification method possesees several advantages. The hexyl alcohol solution of potassium hydroxide and hydrazine is water white and remains so after continuous reflux. The solution can be accurately pipetted. A blank on the reagent had not changed after standing for 12 weeks. A period of 1-hour reflux was sufficient for all esters tested, and in most case6 the saponification is complete within 30 minutes. Dark samples such as FF wood rosin are bleached by the hydrazine to the extent that a phenolphthalein end point is easily seen; accuracy and precision are easily obtained. The alcoholic potassium hydroxide-hydrazine reagent was prepared uqing all of the straight-chain primary alcohols below hexyl. 1345
1346
ANALYTICAL CHEMISTRY
The results of saponifications using these alcohols indicated that such reagents were impractical, inasmuch as increased basicity developed which ir-as titrated at the phenolphthalein end point. However, the hydrazine-potassium hydroxide solution diluted with butyl alcohol or amyl alcohol gave satisfactory results when the test solution was carefully evaporated to dryness a t the end of the saponification, then redissolved in alcohol, and titrated. Methyl dehydroabietate saponified by this method gave a saponification number 177 (theoretical 178.4). K i t h all alcohols below n-amyl, gas was evolved and the blank on the reagent gradually increased on standing. Figure 1 s h o w the merits of using hydrazine in alkali saponification of rosin esters. When solutions less than 0.4V are used a reflux period of 2 hours is required to complete the reaction.
However, 1 hour is sufficient with a 0.4 to 0 . W potassium hydroxide solution. LITERATURE CITED (1) Am. SOC. Testing Materials, Philadelphia, Pa., “ASTM Standards,” Part 111, p. 794, 1942. (21 Ibad.. Part IV. 1). 530. 1949. (3j Redemann, C. E . , and Lucas, H. T., IND.ENG.CHEM.,AS.IL. ED.,12, 187 (1940). (4) Shaefer, TV. E., and Balling, W. J., Anal. Chem., 23, 1126 (1551). (5) Shaefer, TV. E., and Piccard, J., IND.ENG.CHEM.,ANAL.ED., 10, 515 (1938). (6) Simonsen, John, and Barton, D. H. R., “The Terpenes,” vol. 111, p. 413, Cambridge University Press, Cambridge, 1952. (7) Ibid., p. 409.
RECEIVED for review January 26, 1955. Accepted March 16, 1955.
Determination of Cyanide, Thiocyanate, and Alpha-Hydroxynitriles in Plasma or Serum ROBERT 6. BRUCE, JOHN W. HOWARD, and R. Harleton Laboratories, Falls
F. H A N Z A L
Church, Va.
A novel technique is described for the estimation of cyanide, thiocyanate, and a-hydroxynitriles in serum or plasma. I t is based on the conversion of cyanide and thiocyanate into cyanogen bromide which is subsequently reacted with benzidine in pyridine to give an intense color.
I
Ii A study of methods for the determination of cyanide and
thiocyanate ions in biological material it was found that a modification in the technique of the -4ldridge ( 2 ) method would enable the analyst to determine the concentration of cyanide and thiocyanate in serum or plasma separately, rather than calculate the concentration of cyanide by difference as is done by Aldridge. This results in a greater degree of accuracy, especially in the analysis of samples containing trace quantities of cyanide in the presence of large quantities of thiocyanate. APPARATUS
A Beckman Model DU spectrophotometer was used with 1.000cm. cuvettes for light measurements. An aeration apparatus consisting of three test tubes connected in series is shown in Figure 1. Test tubes A (containing 25 ml. of 20% sodium hydroxide) and B are 1 X 8 inches and are fitted with aeration bulbs. Test tube C is 20 X 150 mm. and is fitted with the inlet tube drawn to a capillary tip. Air entering a t E is drawn from a source outside of the laboratory. Vacuum pump 8 attached to D.
Stock Standard Thiocyanate Solution. -40.02N solution of ammonium thiocyanate is prepared and standardized against 0.02N silver nitrate, using iron(II1) alum as indicator. From this stock solution, a series of working solutions is prepared b y dilution to contain from 0.10 to 2.3 y of thiocyanate per 1.0 ml. for preparation of the calibration curves. Pyridine-Benzidine Solution. Immediately before use, 1 part by volume of benzidine hydrochloride solution is mixed with 5 parts by volume of the pyridine solution. PRELIMINARY PROCEDURE
Wave Length Selection. Absorption curves for the colors developed for 2.3 X 10-sM solutions of cyanide and thiocyanate are shown in Figure 2. These curves have the same shape and indicate that the same material is being measured in each case. A maximum in absorbance is present in each at 532 mp. This wave length was therefore selected for maximum sensitivity. Calibration Curve. Calibration curves were prepared for cyanide and thiocyanate by carrying aliquots containing known amounts through the color development procedure exactly as described. The slope of the curve for thiocyanate is 0.281 and R
iL
REAGENTS
Arsenous Acid. A 2.0y0 solution of arsenous acid is prepared by refluxing 2.0 grams of arsenous acid with distilled water until solution is complete. I t is then diluted to 100 ml. Bromine water. A saturated solution of bromine in distilled water is used. Benzidine Hydrochloride Solution. A 4.0y0 solution of benzidine hydrochloride in water is prepared freshly each day. Pyridine Solution. This solution is prepared by adding 100 ml. of concentrated hydrochloric acid t o 1 liter of 60% pyridine in water (v./v.). Trichloroacetic Acid. -4solution of 2OY0 trichloroacetic acid (w./v.) in distilled water is prepared. Stock Standard Cyanide Solution. A solution containing approximately 50 mg. of sodium cyanide in 100 ml. of 1.O.Ysodium hydroxide is prepared. The exact concentration is determined by titrating with 0.02.V silver nitrate using 20y0 potassiuni iodide as indieator. From this stock solution, a series of working solutions is prepared bv dilution to contain froin 0.05 t o 2.0 y of cyanide per 1.0 ml. in 1 . 0 S sodium hydroxide for preparation of the calibration curve. -4s cyanide solutions are very unstable, this solution should be standardized and diliit ed i nmedintely before it is uqed.
Figure 1. A. B. C.
-4eration apparatus
Air washing tube deration tube t o contain sam1ilc Receiving tube D. T o vacuum E. Air inlet R. Ruhher tuhing connections
