T H E J O U R N A L OF I N D Y S T R I A L A N D E L V G I N E E R I N G C H E M I S T R Y
482
carefully investigated a n d a t no t i m e did we find a n increase i n t h e percentage of t h e d r y gluten due t o t h e increase in t e m p e r a t u r e . I n order t o t e s t t h e effect of t e m p e r a t u r e on t h e washed glutens t h e y were allowed t o s t a n d twelve hours a t 2 5 ' C., having veen washed a t 15' C. T h e glutens h a d become very sticky a n d h a r d t o d r y . T h e low grades all showed t h a t fermentation h a d s t a r t e d . T h e low grades showed a marked decrease while t h e high grades showed only a slight decrease. T h i s was also t r u e of t h e dry glutens. Whatever agency causes t h e increase in weight, when t h e t e m p e r a t u r e of t h e wash water is higher t h a n ordinary, is within t h e flour itself a n d is n o t contained in t h e wet gluten. A higher percentage of gluten is obtained b y washing i n h a r d water t h a n i n s o f t . Hardy' is of t h e opinion t h a t electrolytes or salts, which m a y be organic or inorganic, impress t h e property of tenacity a n d ductility on t h e gluten. Wood's2 researches also prove t h a t inorganic salts have a binding effect on gluten. All authorities agree t h a t gluten cannot be washed f r o m flour with p u r e distilled water because t h e gluten will n o t hold together. A t first i t forms a coherent mass b u t as soon a s t h e salts, n a t u r a l t o t h e flour, are dissolved, t h e gluten scatters a n d cannot be collected again. If it be submerged i n h a r d water when it first s t a r t s t o s c a t t e r it forms again a coherent mass. T h e r e was a n increase of I t o 2 per cent in wet gluten for all grades when t h e glutens were washed i n very h a r d water. There was only a slight change of a b o u t 0 . 2 5 per cent for t h e d r y gluten a t t h e most, showing t h a t t h e h a r d water usually increased t h e waterabsorbing capacity of t h e gluten. C 0N CLUS10 N S
It c a n readily be seen t h a t conditions m a y be so different i n various laboratories t h a t t h e determinations of wet gluten are n o t comparable. E r e n for ordinary routine work, where comparative results alone are required, unless t h e u t m o s t care is t a k e n , t h e determination is unreliable. Since t h e percentage of d r y gluten is very slightly affected b y these same conditions i t is more reliable. I-Thoroughness of mixing affects b o t h t h e per cent of wet a n d d r y gluten. 2-An excess of water used in making t h e doughs increases, a n d insufficient water decreases t h e per cent of wet gluten. T h e d r y gluten is t h e same. 3-The length of t i m e t h e dough is allowed t o stand increases t h e percentage of wet gluten up 50 eight hours. High p a t e n t s , old flours a n d low grades are exceptions. T h e d r y gluten remains unaltered except in t h e low g r a d e where some fermentation h a s t a k e n place. 4-Overwashing decreases t h e percentage of b o t h t h e wet a n d d r y gluten. 5-A larger per cent of wet gluten is obtained with w a r m wash water t h a n with cold. T h e d r y gluten is unaffected. 6-More wet gluten is obtained with "hard" wash 1 2
Supplement J o u r , 4 (1910), 5 2 ; Jour. Board of A g r t c . Jour. A g r i c . S c i e n c e , I (1907). 267.
Vol. 6, NO. 6
water t h a n with soft. T h e d r y gluten is slightly increased b y t h e h a r d water. FLOURTESTING LABORATORIES C o , LTD. MAPLELEAF MILLING PORTCOLBORNE. ONT.
XX-HEAT A N D
THE DETERMINATION OF THE ACETYL NUMBER OF OILS, FATS, ETC.' By EDWARD B HOLLAND Received January 13, 1914
Ih*TRODUCTIOX
T h e various hydroxy compounds t h a t occur in oils, f a t s a n d waxes form derivatives on heating with acetic a n h y d r i d e , the acetyl radical displacing t h e hydrogen of t h e alcoholic hydroxyl groups. This property serves as t h e basis of analytical methods for t h e q u a n t i t a t i v e determination of these compounds. T h e proposed acetyl number indicates t h e milligrams of potassium hydroxide required for t h e saponification of t h e acetyl assimilated b y one g r a m of a n oil, f a t or wax on acetylation.2 On saponifying with alcoholic p o t a s h t h e acetyl is hydrolyzed t o acetic acid a n d combines with t h e alkali t o form potassium acetate. T h e results are expressed i n t e r m s of milligrams of potassium hydroxide t o conform with t h e general practice in f a t analysis. T h e compounds involved are mono- a n d dihydroxy acids a n d their glycerides, mono- a n d diglycerides a n d free alcohols. USE O F T H E TEST
I n t h e examination of oils a n d f a t s a determination of acetyl number is necessary, in most instances, for a thorough understanding of t h e n a t u r e a n d quality of t h e product. Some of t h e hydroxy compounds are n a t u r a l a n d others are t h e result of hydrolysis or of oxidation. Glycerides of hydroxy acids a r e a n a t u r a l constituent of certain oils a n d f a t s although t h e y d o n o t appear t o be very widely distributed i n a n y considerable a m o u n t . Castor oil, composed largely of ricinolein, is a notable illustration. H y droxy acids probably occur more frequently as t h e result of oxidation of u n s a t u r a t e d acids. Oleic acid has been shown repeatedly t o be comparatively u n stable. By t h e assimilation of oxygen a n d water i t m a y be converted i n t o dihydroxystearic acid, a s a t u r a t e d compound. C1;HssCOOH H20 0 = Ci?H33(OH)gCOOH. Whether t h e oxidation t a k e s place i n t h e glycerides or i n t h e f a t t y acids afte'r hydrolysis is uncertain, although t h e l a t t e r appears t h e more probable supposition. 5lono- a n d diglycerides result from t h e hydrolysis of triglycerides a n d free f a t t y acids condition their presence. T h e absence of free f a t t y acids in a commercial product, however, does not necessarily preclude t h e presence of mono- a n d diglycerides. Solid alcohols of t h e cyclic series (sterols) occur in oils a n d f a t s b o t h in combination as esters a n d a s free
+
+
1 The writer is pleased t o acknowledge many suggestions and helpful criticisms by Dr. J S Chamberlain, Mr. F. W. Morse, Mr J. C Reed, and Mr. J. P. Buckley. 2 Benedikt and Ulzer and Lewkowitsch report on the basis of the acetylated product.
J w e , 1914
THE JOL'R-VAL O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
alcohols.' T h e a m o u n t of cholesterol or phytosterol is generally small, often inappreciable, a n d is indicated approximately b y t h e unsaponifiable m a t t e r which i t characterizes. Alcohols of t h e ethane a n d other skries, free a n d i n combination, compose a considerable proportion of waxes. Oils a n d f a t s , therefore, m a y contain glycerides of mono- a n d dihydroxy acids, possibly free hydroxy acids. mono- a n d diglycerides a n d free alcohols; a n d t h e insoluble acids, separated from t h e oils a n d fats, m a y contain mono- and dihydroxy acids a n d free alcohols. A portion, at least, of t h e free alcohols found in t h e insoluble acids probably occurred in t h e f a t a s esters. W i t h t h e exclusion of t h e n a t u r a l glycerides of hydroxy acids a n d a small a m o u n t of free alcohols, t h e acetyl number of m a n y oils a n d fats m a y be deemed a n index of quality a n d when considered i n conjunction with t h e acid a n d iodine numbers, may serve t o measure (more or less imperfectly t o be sure) t h e a m o u n t of hydrolysis a n d of oxidation t h e product has undergone. T o differentiate between products of hydrolysis a n d of oxidation, t h e acetyl number of t h e insoluble acids should also be determined. E A R LI E R 11E T H 0 D S
483
ural product. I n conformity thereto the acetyl number indicates t h e milligrams of potassium hydroxide required for t h e neutralization, of t h e acetic acid obtained on saponifying one gram of a n acetylated oil, fat or wax. This method requires t h e saponification of t h e acetylated f a t a n d t h e determination of t h e resulting acetic acid b y either a filtration or distillation process. T h e former process is an adaptation of t h e regular method for the direct determination of soluble acids, a n d t h e l a t t e r process is a modified Reichert-Neissl t e s t with repeated distillation of t h e aqueous solution until t h e distillate is free from acids. T h e presence of n a t u r a l soluble or volatile acids necessitates a similar t r e a t m e n t of t h e unacetylated f a t i n order t o determine t h e a m o u n t of alkali assimilated b y those acids for which proper corrections must be m a d e t o ' o b t a i n t h e t r u e acetyl number. T h e occurrence of t h e lower acids makes t h e determination a long a n d tedious operation. P R 0P 0 S E D MET H 0 D
Analytical methods for t h e examination of oils and! f a t s is a subject t h a t has been given considerable s t u d y b y t h e writer in connection with feeding experiments a n d other investigations made a t t h e Massachusetts Agricultural Experiment Station. During t h e past fern years t h e determination of acetyl n u m b e r h a s received particular a t t e n t i o n with a view of evolving a process t h a t might be free from t h e objections cited for t h e Benedikt a n d Ulzer a n d Lewkowitsch methods. Believing t h a t this object has been obtained in some measure, a report of progress is now offered in t h e hope t h a t it m a y lead t o further improvement. T h e custom of reporting acetyl number on t h e basis of t h e acetylated product appears unwarranted. I t is contrary t o general practice i n analytical work a n d is t h e exception in fat analysis. T h e definition' adopted places t h e acetyl number on a par with other tests a n d is as follows: T h e acetyl number indicates t h e milligrams of potassium hydroxide required for t h e saponification of t h e acetyl assimilated b y one g r a m of a n oil, f a t or wax on acetylation.
The several analytical processes t h a t h a v e been offered are based on t h e s a m e chemical reactions b u t differ in application a n d i n details of procedure. T h e original method was devised b y Benedikt a n d Ulzer? a n d applied t o t h e insoluble acids. T h e acetyl number indicated t h e milligrams of potassium hydroxide required t o neutralize t h e acetic acid obtained on saponifying one gram of acetylated insoluble f a t t y acids a n d was determined b y t h e difference between t h e acid a n d saponification numbers of t h e acetylated acids (acetyl ether n u m b e r ) . T h e actual procedure consisted i n saponifying t h e acetylated acids after neutralizing i n alcohol. L e w k o ~ i t s c h ~has shown, however, t h a t t h e results so obtained were generally i n excess of t h e t r u e values d u e t o t h e conversion of a p a r t of t h e f a t t y acids, on heating with a large excess of acetic anhydride, i n t o their anhydrides a s illusMETHOD IK D E T A I L t r a t e d b y t h e following equation: T h e development of t h e method extended over a 2RCOOH (CH,CO),O = ( R C 0 ) z O Z C H ~ C O O H period of several years a n d finally resoli-ed i n t o a n fatty acetic anhydride of acetic a d a p t a t i o n of several well linown processes. For acid anhydride f a t t y acid acid instance, ceresine is used t o solidify t h e acetylated f a t These f a t t y anhydrides are fairly stable compounds so t h a t it m a y be washed b y decantation as in t h e b u t m a y become hydrolyzed t o some extent on washing determination of insoluble acids. T h e saponification with boiling water. Subsequent t r e a t m e n t with cold numher of t h e acetylated f a t is determined b y t h e alcohol in t h e determination of t h e acetyl acid n u m - same process a s t h a t of t h e original f a t a n d t h e differber will continue t h e hydrolysis although a portion ence measures t h e a m o u n t of acetyl t h a t has been is likely t o remain unchanged, t h e r e b y yielding too assimilated. The process m a y be appropriately delow a n acid number due t o t h e inability of t h e an- scribed as a method of analogy. hydrides t o combine with alkali. Xs complete h y T h e reagents employed in t h e deterinination are drolysis occurs on saponification t h e acetyl (ether) summarized so t h a t their application may be clearly number would be too high a n d even appear when understood: none exists. Acetic anhydride, Kahlbaum's. Lewkowitsch4 proposed t h e acetylation of t h e n a t Ceresine, pure white, filtered. Abderhalden, "Physiological Chemistry," 1 See numerous references: .%lcohol, redistilled, free from acids and aldehydes. (1908); Hammarsten, I b i d . (1911); Leathes, "The Fats" (1910). Alcoholic potash, 50 cc. of a saturated solution of potassium Monotsh. Chem., 8 ( 1 8 8 7 ) , 41-48.
+
+
2
3 4
"Analysis ol Oils, F a t s and \%'axe.;," 1 (19091, 344-5. LOC.c i t . , 1 (1909). 337-8.
1 T h e hydroxyl value of Twitchell is reported in a similar manner. J o z r . .Arne?. C h e m . .Soc., 29 (190;). 566-71.
.
484
T H E JOL7RNAL OF INDI'STRIAL
hydroxide, free from carbonate, to 1000 cc. of alcohol. The solution should be allowed to stand a t least 24 hours and filtered immediately before use. N / z hydrochloric acid. Alkali blue (6B), I gram to IOO cc. of alcohol. The indicator should be digested in a stoppered bottle for several days a t room temperature, with occasional shaking, and then filtered. Phenolphthalein, I gram to IOO cc. of alcohol, neutralized. After w h a t h a s been said, t h e details of t h e method should be sufficiently evident as t o require n o f u r t h e r explanation. Into a 300 cc. Erlenmeyer flask are brought j grams of fat together with I O cc. of acetic anhydride. The flask is connected with a spiral or other form of reflux condenser and heated in a boiling water bath (immersed in the water) for from I to 1 . j hours. Longer heating yields higher results but is accompanied by partial decomposition of the fat with formation of aldehydes or other bodies that give a reddish color with caustic alkali. After acetylating, the flask is removed from the bath and sufficient ceresine added to form, with the fat, a solid disc when chilled in cold water. The amount of ceresine required will vary with the consistency of the product under examination. For butter fat 0.4 to 0 . 5 gram is ample, for softer fats and oils rather more, and for harder fats less. The ffask is heated on the water bath and the contents rotated until the ceresine and acetylated fat form a homogeneous mixture. I j o cc. of boiIing water are then poured carefully into the flask with as little disturbance of the fat layer as possible and the solution heated on the bath with occasional agitation to remove occluded acetic acid. The flask is immersed in cold water to solidify the ceresine fat, after which the solution is decanted through a dense, etherextracted filter, care being taken not to break the insoluble cake, Another I j o cc. of boiling water are added, thoroughly agitated, heated as above, cooled and decanted, the process being repeated until the final filtrate gives a decided color with z or 3 drops of N,I O alkali, using phenolphthalein as indicator (about 6 times). Prolonged washing is likely to cause slight dissociation of the acetylated product. The filter and inverted flask containing the cake of ceresine-fat are allowed to drain in a cool place until practically dry. The small particles adhering to the filter are then scraped into the flask, and 50 cc. of alcoholic potash, accurately measured with a burette, j o cc. of alcohol and several glass beads added. The flask is connected with a spiral or other form of reffux condenser and the solution boiled on a water bath until saponification is complete-about 60 minutes. The flask is placed in a water bath a t 60' C. and the solution, after cooling to that temperature, titrated with N l ' z hydrochloric acid, using I cc. of alkali blue as indicator. Phenolphthalein may be employed, though less satisfactory for colored solutions. The alcoholic mixture is again brought to boil to free any alkali occluded in the ceresine and retitered, if necessary. Several blank determinations should be run with every series of tests under precisely similar conditions as to time and treatment except that the ceresine may be omitted. However, every lot of ceresine must be tested, should be free from soluble matter and not assimilate any alkali on saponification. The difference between the titration of the blank and that of the excess alkali in the test is the acid equivalent of the fat after acetylation, which should be calculated to milligrams of potassium hydroxide for I gram of fat. I ce. of N / 2 acid is equivalent to 28.054 milligrams of potassium hydroxide. The difference between the saponification number of the fat before and after acetylation is the acetyl number. I n case the original fat contains free soluble acids, their titer should be determined and proper correction made for the same. Limit of error 0.j o acetyl number.
SYSOPSIS O F REACTIOS
4 b e t t e r conception of t h e method m a y be o b t a i n e d b y a s u m m a r y of t h e reactions. Acetylation of glycerides of mono- a n d dihydroxy acids, mono- and diglycerides and free alcohols (see formulas). Saponification of the acetylated product (see formulas). Saponification of the original or unacetylated product. Titration of excess alkali. Acetyl number b y difference.
DIHYDROXY ACInS A c e t ) laiion (R.OH.C00)aC3Hj 3!CHaCO)zO = (R.OCH.?CO.COO)pC3Hj 3CHzCOOH triglyceride of acetic acetylated acetic monohydroxy acid anhydride glyceride acid EXAMPLE:Ricinolein, ( C L ; H ~ ~ . O H . C O O ) S C ~ H ~ Saponification (R.OCHaCO.COO),C3Hj 6KOH = alkali 3R.OH.COOK 3CH3COOK f CrHs(0H)a acetylated potassium potassium glycerol salt of acetate glyceride hydroxy acid GLYCERIDES OF
M O N O - AND
+
+
-
+
[R(OH)zCOO]aC3Hj triglyceride of dihydroxy acid
T
+
ICHICOjrO = [ R ( O C H I C O ) P C O ~ ] ~ C ~ HHrO ~ acetylated glyceride
EXAMPLE: Dihydroxystearin, [C,,Ha3(OHj?C0013CIHi [R(OCH~CO)?COO]ICJH; + 9KOH = 3R(OH)sCOOK 6CHrCOOK f CaHi(OHj; MONO-A N D DICLYCERIDES (RCOO)CaHj(OH)z (CH3CO)zO = (RCOO) (CHaCO0)rCaHi H?O monoglyceride diaceto-glyceride
+
+
+
(RCOO)(CH3COO)lCaHj (RCOO)?CaH:(OH) diglyceride
-
- 3KOH
=
+
+
RCOOK 2CHsCOOK CsHj(OH)3 (CH3COlzO = (RCOO)t(CH3COOjCrHj 4-C H K O O H monoaceto-glyceride
(RCOO)*(CH3COO)CaHj
- 3KOH
=
ZRCOOK f CHjCOOK
- CsHj(OHlr
FREEALCoEI0I.S R O H t (CH3CO)lO = CHaCOOR f CHrCOOH acetate monobasic alcohol of alcohol CHiCOOR KOH = R O H CH3COOK
+
+
EXAMPLES: Cholesterol, phytosterol, C?:Hl:OH
Considerable variation is possible in writing t h e a b o v e formulas which, a t b e s t , poorly express t h e s t r u c t u r e . In some instances t h e reaction is indicated a t some sacrifice of form. CALCULATED DATA F R O M T H E ACETYL I i U h f B E R
T h e acetyl n u m b e r (c) serves t o measure t h e a m o u n t of h y d r o x y compounds i n a n oil, fat or wax a n d i n case only one such compound of known molecular weight ( m ) a n d n u m b e r of hydroxyls (d) is present, i t s a m o u n t ( H ) c a n be readily calculated b y t h e follon-ing f o r m u l a : c in H = j61oXd ~
T h e derivation of t h e formula is comparatively simple. T h e theoretical acetyl n u m b e r of a comp o u n d containing (d) hydroxyl groups is: .j 6 I o8d
fn T h e a m o u n t of such a compound i n a n oil, f a t o r wax is, therefore: C
j6108d m
-
cm ~
j6108d
T H E JOL7RS.iL OF I S D l * S T R I d L . I S D ESGIAVEERISG CHEJIISTRI’
June 1914
T h e same results m a y be calculated more easily from t h e following table, dir-iding t b e determined acetyl number b y t h e theoretical acetyl number or multiplying b y i t s reciprocal: .%CETYL
3 1 \ l B E R O\
T h e formation of anhydrides during t h e acetylating process will affect t h e accuracy ot these calculations T h e computation of t h e a m o u n t of hydro.;! com-
~ ) R l C l h A LPRODLCT
lI4S5sCHLSETTS I\IET€lOD
For mu la
hiolecular (:LYCERIDES weight 932.832 Ricinolein, (CI:H3?.0H.C00)3C3H; . . . . . . . . . . . . . . . . . . . . . Dihydroxystearin, [C1:Hs3(OH)rC001]C3H.. . . . . . . . . . . . . . . . . 986.880 ?.IOSOGLYCERIDES hlonopalmitin. ( C L S H ~ I C O O ) C ~ H ~ (.O. H. ~. :. . . . . . . . . . . . 330.304 Monostearin, ( C 1 ; H K O O j C i H ~ ( O H ) r . . . . . . . . . . . . . . . . 358 336 . . . 356.320 Rfonolein. I C I ; H ~ ~ C O O ~ C : H ~.( .O. H . . ~. .~.. . . . . . . . . . . . . DIGLYCERIDES Dipalmitin, ( C L S H ~ I C O O ) ? C ~ H ~. (.O.H. ~. . . . . . . . . . . . .. . . . . 568.544 Distearin, fC),:H3~C00)2C3Hj(OHj . . . . . . . . . . . . . . . . . . . . . . 624.608 . . . 620.576 Diolein. ( C ~ ~ H ~ ~ C O O ) Z C Z H. .~. (. O . .H. .) .. . . . . . . . . . . . . . . . HYDROXY .%CIDS Ricinoleic, C I ; H ~ . O H . C O O H.. . . . . . . . . . . . . . . . . . . . . . . . . ,. 298,272 Dihydroxystearic, C I ; H ~ ~ ( O H ~ Z C O O . .H. ... . . . . . . . . . . . . . . . . . . 316.288 Same
485
Saponification number 180.444 170.562
Theoretical acetyl number 180.444 341.121
0.00293 15
169.868 156.575 157.465
339,736 3.13. I59 314.930
(I.002543i 0 0031531 0 0031753
197.374 175.658 180.826
98.687 89.829 90.413
188.110 177.395
354.791
0.0053160 0 0028186
145,219 145,219
0.0068862 0.006886?
Reciprocal 0 005541Y
o
oi01~30 0 . 0 I I1323 0.0l10604
188.l10
F R E E .~LCOHOLS
Cholesterol, C Z H I J O H . .. . . . . . . . . . . . . . . . . . . . . . . . . . . Phytosterol, C K H J ~ O H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GRAVIMETRIC
PROCESS
-4fter acetylating. a gravimetric process for acetyl number m a y be conducted in a manner similar t o t h a t for t h e quantitative determination of insoluble f a t t y acids, observing all t h e precautions therein noted as t o ceresine. washing, drying. weighing, etc. This modification is apparently rather more difficult. tedious a n d subject t o error t h a n t h e saponification or volumetric process (Massachusetts method). A certain a m o u n t of loss arises from t h e dehydration of free f a t t y acids b y acetic anhydride during acetylation. a n d is difficult t o prevent. although of little consequence n-here t h e a m o u n t of free acids is relatively small. T h e acetyl number ( a ) is calculated from t h e increase in weight (i) b y . t h e following formula: j6108i a = or 133 j.39604i 42.016 I n case only one hydroxy compound of known molecular weight (7%) a n d number of hydroxyls ( d ) is prese n t , i t s a m o u n t can be calculated from t h e increase in weight (i) of t h e oil, f a t or wax on acetylating. T h e theoretical increase for a hydroxy compound is: 42.016d Vi
T h e a m o u n t ( H ) of such a compound in a n oil, f a t o r w a x is therefore: i vz H = -2 or 42.0 I 6 d 42.0 i 6 d ~~~~~
rta 1\IOLECKLAR 1VI:IGHT
O F HYDROXY C O X P O U S D S
T h e molecular weight of t h e hydroxy compounds can be calculated from t h e !!-eight (w)of f a t t a k e n a n d t h e increase (i) on acetylating. provided t h e number ( d ) of hydroxyls in t h e molecule is known: L ‘ :
zt
+i
=
nz =
m :
?PI
+-
42.016d
4 2 .or6d.*8 -~
~~~
i
H a s not received sufficient study in this laboratory t o warrant positive statements, b u t is similar t o the methods described b y Lewkoaitsch (Loc. c i l , 1, 358-63, 466-67). 1
.. 386.368 . _ . 386.368
.....
.....
pounds b y t h e gravimetric process is greatly facilitated b y use of t h e following t a b l e : ACETYL GRAVIMETRIC PROCESS
hlolecular Same weight GLYCERIDES Ricinolein.. . . . . 932.832 Dihydroxystearin. 986.880 XIOsOCLYCERlDES hlonopalmitin. . 330.304 hlonostearin.. . . . . . 358.336 Alonolein . . . . . . . . 356.320 DIGLYCERIDES Dipalmitin.. . . . . 568.544 Distearin. . . . . . . . 624.608 Diolein., . . . . . . . 620.576 HYDROXY AcIns Ricinoleic , . . , , , , 258.277 Dihydroxystearic. . 3 16.288 FREEA ~ c o i r o ~ s Cholesterol.. . . . . . 386.368 Phytosterol , . , . , , , 386.348 ( a ) Acetyl number
PRODL-CT Theoretical increase in Jlolecular rreight pcr weight after gram on acetylating acetylatingiu) Reciprocal OS oRlGIXAL
1058.880 1238.976
0.255447
7.40061 3.91471
414.334 447.368 440.352
0.254408 0 234506 0.235833
3,93069 4.26428 4.24029
610 560 646.624 662.591
0.073901 0.067268 0 067705
13.53167 11.8659 I 14.76996
340.288 400.320
0.14086S
0.265682
7 .05500 3.76390
0.108746 0.108746
9.19574 9 . I9ji-i
428.,384 428.384
0.135124 I
1335.396041.
A C E T Y L S V J I B E R O F I S S O L L - B L E F A T T Y ACIDS
T h e acetyl number of t h e insoluble f a t t y acids is determined b y t h e Nassachusetts method in precisely t h e same way as t h a t of t h e original f a t . The gravimetric process is not applicable on account of t h e formation of anhydrides of t h e f a t t y acids. T h e method for preparing t h e stock of insoluble acids for analysis is t h e same a s t h a t for t h e determination of “Insoluble Xcids,” with t h e elimination of such features as are necessary only for quantitative work. I n order t o interpret t h e results satisfactorily it is necessary t o know t h e percentage of insoluble acids so t h a t t h e acetyl number of the acids m a y be considered in conjunction with t h e acetyl number of the f a t . RESVLTS B Y D I F F E R E K T METHODS
For convenience, t h e theoretical acetyl numbers of some hydroxy compounds b y the Benedikt a n d Ulzer and Lewkoxitsch methods are tabulated t o permit comparison with t h e acetyl numbers b y t h e LIassachusetts a n d gravimetric processes previously s t a t e d . When only one hydroxy compound of known com-
T H E J O U R N A L OF I A V D U S T R I A L A N D E - V G I - V E E R I X G C H E M I S T R Y
486
Pol. 6 , KO. 6
ACETYLNCMBERO N ACETYLATED PRODUCT. BENEDIKTASD ULZER A N D LEWICOWITSCH METHODS Name (Acetylated) Formula GLYCERIDES ... Ricinolein, (CliHa?.OCH~CO.C00)3C3Hs,. . . . . . . . . . . ... Dihydroxystearin, [ ClrH3a(OCHaCO)zC00]3C3Hs.. . . . MONOGLYCERIDES Monopalmitin, (CisH31C00) (CHaC00)zCaHj. . . . . . . . . . . . . . . ... Monostearin, (CliHasC00) (CHaCOO)?CaHs . . . . . . . . . . . . . . .. . . . . . ... Monolein, ( C i i H d 2 0 0 ) (CH3COO)zCaHs. . . . DIGLYCERIDBS ... Dipalmitin, (CisHaiCOO)z(CH3COO)CaHs.. . ... Distearin. (C~7HasCOO)z(CHaCOO)CaHs. ... ...... Diolein. ( C ~ ~ H ~ ~ C O O ) Z ( C H I C O O . . ). C . .~ H ~ . HYDROXY ACIDS Ricinoleic, Ci7H3z.OCH3CO.COOH. . . . . . . . . . . . . . . . . . . . . . . .. . .. . . .. , Dihydroxystearic, Ci7Haa(OCHaCO)zCOOH. . . . . . . . . . . . . . . . . FREEALCOHOLS ... Cholesterol, CHaC0OCz;His.. . . . . . . . . . . . . ... Phytosterol, CHsCOOCnHij.. . . . . . . . . . . . . .
...
position is present i n a n oil or f a t , t h e results can be readily converted f r o m t h e basis of t h e original t o t h a t of t h e acetylated p r o d u c t a n d v i c e versa. In o t h e r cases conversion is generally impracticable on account of t h e m a r k e d differences in assimilation of a c e t y l b y t h e several classes of hydroxy compounds. F o r m u l a s m a y show t h e relation, however, t h a t t h e results b y different m e t h o d s bear t o each o t h e r , ( m ) indicating t h e molecular weight of t h e h y d r o x y comp o u n d , ( d ) t h e n u m b e r of hydroxyls, a n d (i) t h e increase i n weight on acetylating:
Massachusetts Method Cm
j6108d
Graaimetvic M e t h o d im 42.016d
B c ) I e d i kt a pad U l z er a n d L e w k o zit sc h Jd et h o d s c(m
+ 42.016d)
j6108d S C X I 414 R Y
T h e acetyl n u m b e r s of a f a t a n d of t h e insoluble acids afford valuable information relative t o t h e n a t u r e a n d t h e quality of a product. i l p p a r e n t l y m a n y a n a l y s t s h a v e been deterred f r o m making t h e det e r m i n a t i o n s o n account of t h e t i m e required, tedious manipulation involved or inability t o i n t e r p r e t t h e results. T h e proposed m e t h o d is comparatively s h o r t a n d simple a n d readily understood because of its similarity to o t h e r f a t m e t h o d s i n common use. It is practically free f r o m t h e objections cited for t h e earlier m e t h o d s a n d t h e results a r e directly comparable with other f a t determinations, being on t h e s a m e basis. MASSACHUSETTS AGRICULTURAL EXPERIMENT STATION AMHERST
Molecular weight
Saponification number
Theoretical acetyl number
Reciprocal
1058.880 1238.976
317. 928 407. 5 7 2
158.964 271.715
0 0062907 0 0036803
414.336 442.368 440.352
406.250 380 507 382.249
270.833 253.67 1 254.832
0 0036923 0 0039421 0 0039242
610.560 666.624 662.592
275.688 252.502 254.039
91.896 84.167 84.680
0 0108819 0 0118811 0 0118092
340.288 400.320
329.768 420.474
164.884 280.316
0 0060649 0 0035674
428.384 428.384
..... .....
130.976 130.976
0 0076350 0 0076350
obtained b y n e u t r a l a m m o n i u m citrate. This f a c t was f u r t h e r confirmed b y us i n t h e determinations o n a sample of acid p h o s p h a t e shown i n T a b l e I. These determinations were m a d e substantially according t o t h e official m e t h o d s of t h e A . 0. A . C.,I except t h a t t h e neutral a m m o n i u m citrate solution was prepared as described in our previous paper.2 T h e phosphoric acid was i n all cases determined b y t h e volumetric nlolybdate m e t h o d . T h e proportions of reagent, whether n e u t r a l a m m o n i u m citrate, sodium citrate or S ' I O citric acid, t o t h e weight of sample t a k e n , were t h e same a s i n t h e official m e t h o d . TABLE I-DETERMINATIONOF
I N S O L U B L E P H O S P H O R I C ACID WITH SODIUM CITRATEA N D NEUTRALAMMONIUM CITRATE Sodium c i t r a t e . . . . . . . . 1.467, Ammonium c i t r a t e . . . . . . 0.30$, 1.42 0.34 A v . . . . . . . . . . . . . . . . 1.44 0.32
T h e specific g r a v i t y of t h i s sodium citrate solution was 1 . 1 6 3 as against 1 . 0 9 for n e u t r a l a m m o n i u m citr a t e solution. Various trials showed t h a t more conc e n t r a t e d solutions of sodium citrate give results a p proaching more nearly those obtained b y t h e use of n e u t r a l a m m o n i u m citrate, a s shown i n T a b l e 11. TABLE11-DETERMINATIONOF
INSOLUBLE PHOSPHORIC ACID I N ACID VARYING CONCENTRATIONS O F S O D I U X CITRATE A S COMPARED WITH .4MMONIUM CITRATE Percentages Specific 7 G. Der 1. eravitv 1 2 3 4 Ammonium c i t r a t e . , . . . . . . . . . 1.09 0 . 5 3 2.58 0 . 7 7 0.62 2.62 . . 0.65 Sodium citrate, . . . . . . . . . 80:0 1 043 1 1 83 159.5 1.084 , . 3:i4 '. l i 8 . 5 1.093 . . . . . . 1.53 . . . . . 1.59 24>:7.1.123 , . 3:06 .. 2 9 3 . 8 1.147 . . . . . . 1.28 . . 1.3i 312:81:i53 2:90 . . . . 326.6 1.163 . . . . . . . . 4 4 3 . 0 1.220 2.92 . . . . 496.8 1.231 0:92 .. .. 5 6 8 . 8 1.282 , , . . 0:49 , , . . . . . . . . . . 0.46 . .
PHOSPH.4TE
WITH
I
_
;
:: ::
::
A COMPARISON OF NEUTRAL AMMONIUM CITRATE WITH SODIUM CITRATE AND N I O CITRATE ACID'
SOTS-The concentration of sodium citrate is expressed in grams of crystallized sodium citrate [ (CsHsOiKaa)~.1 1Hz01 per liter.
By PAULRUDNICK,W. B. DERBY A N D W. I,. LAISHAW
T h e disadvantages of working with such h e a v y solutions suggested t h e possibility of using a citric acid solution of suitable concentration a s a s u b s t i t u t e . After t r y i n g various s t r e n g t h s ranging f r o m t w o per cent, as used, for basic slag analyses, downward, i t was f o u n d t h a t a :V;V,.IO solution of citric acid g a v e results approximating q u i t e closely t o those obtained with n e u t r a l a m m o n i u m citrate. T h e results are shown i n T a b l e 111.
Since t h e appearance of a previous p a p e r 2 on t h e subject of n e u t r a l a m m o n i u m citrate, t h e use of sodium c i t r a t e a s a s u b s t i t u t e for a m m o n i u m citrate h a s been proposed b y B o ~ w o r t h . ~T h e values obtained b y h i m with a solution of sodium citrate of t h e s a m e molar concentration a s t h e official a m m o n i u m citrate solut i o n a r e , however, n o t i n good concordance with those 1 Presented a t the 49th Meeting of the American Chemical Society, Cincinnati, April 6-10, 1914. 2 THISJOURNAL, 6 (1913), 1013. 3 I b i d . , 6 (1914), 227.
1
Rev. Bur. of Chem.. Bull. 107, pp. 1-5. THISJOURNAL, 5 (1913), 1013.
