V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2
DISCUSSION OF
RESULTS
Invariably, in thc case of carotene, losses were accompanied by the formation of pigment which was held relatively firmly by CeMe against elution by Skellysolve, but, was removed by Skellj,solve containing 470 ethyl alcohol by volume. T h e increased affinity of this pigment for Celi'ce suggests t h a t i t is oxidized carotene. When loss of carotene did occur upon exposure t o Celite, t h e absorption curve for the recovered pigment also clixnged; the sbeorbancy a t 430 nip increased, and that a t 480 mp decreased, relative t o the absorbancy at 450 mp. This change in abjorption ratios is caused mainly by isomerization of carot.ene bj- Hyflo Super-Cel along with oxidation as judged from dat,a in Tahle 111. Fractions 7 and 8, in view of their adsorbent tenacity, are deemed oxidation products. In routine chromatographic analyses of carotene in Skellysolve with Celite, or Celite-adsorbent, mixtures, i t is conceivable t h a t tlestruction or alteration of pigment may be negligible when time of fikration is short, 2 to 5 minutes: however, in longer filtrations, especially in the separation of isomeric constituents, the tendency of Celite to isomerize and oxidizc carotene cannot be ignored .blutein. in all instanceP iqmrted in Tahle V, failed to give
683 the original r2ttios of absorbancies, this pigment is evidentlv easily altered b v contact with Hyflo Super-Cel. Although the amount of destruction or alteration can be markedlv decreased by use of ammonia-treated Celite, bv operation a t 0" C., or by use of acetone, none of these devices or cornbinations reported in Table V gave complete recovery of unaltered lutein. In separation or andvsiq of lutein, the usc of CelitP should he attended with reservAtions LITERATURE CITED
Bickoff, E. \ I . , White. L. \I., Hex-enue, -4.. arid Xl-illiams. I- s:rniplt~ into the sensitive range, so that any (*oncentration including pure hc111z~.l alcohol can be determ i n d . T h e s a ~ n p l need e not he soluble in water in all proport,ious. Any dilution t h a t fails to give complete solution should be omitted :md only tlilutioli:: that give homogeneous solutions ~1iouIdbe t,wted further. If the :tpproxini:ite concentration is
known, it is sufirient to test only t h e dilution th:tt applies to t h a t concentratioti. Table I gives the proper dilution for each concentration range of benzyl alcohol and the factor by n.hich the reading from the graph should be multiplied in order to determine the concentration of benzyl alcohol in the original sample. After dilut,ing t h e sample t o obtain ni:iximuni sensitivity, transfer 5 nil. t o a colorimeter t,ulie and continue as in t,he calibration of t h e photelometer. To obtain the Iienzyl alcohol concentration of t h e sample, multiply t h e wading from the graph t)y the factor lihted in Table I. If a suhstnnce is present whose aqueous solution darkens on heating with sulfuric acid, it may he po,wible t o ovei'(*oniethe interference hy selective extraction h d o r e aixtlyais. If B su1)st:tnce is present v-hose sulfate is inpoluhle, such :ts lead or Imiuni, t h r sample should he h a t e d n.ith :i reagent, poasibl~. sodium carhonate, t o remove t h e interfering sul)st:tnce before sulfuric acid is added. PRECIS103 4 Y D S E N S I T I V I T Y
Tai)le I1 slion-s the prerisioii obtained n licn threcx mixes of benzyl alcohol were made up at enrh c~oiic.fiiti.:itioiiand mal! was run in quadruplicate, giving it total of t\vc.lvr tests at each concentration. T h e average per c*ctit stnticl:ird deviation \vas found to he :ibout &37, for wnwntrtttionP of h n z y l alcohol above 0.10 nil. per liter. If thcx cwiirt~iitratiotiis less than 0.10 ml. of h ~ ~ n alcohol z ~ l per liter of solution. t h c ~preckion dwreases rapidly \\-itti tlrop in concentrittioii. LITER.4TLRE CITE11
(1) Callaway, Joseph. Jr., and Reziiek. Solomon, .J. As.suc. Ofic.d g r . Chemists, 1 6 , 285-9 (1933). ( 2 ) Vohler, H., and Himmerle, IT.,,Uitf. Lehozsm. H,yg., 30,284-320
(1939j .
( 3 ) JIohler. H.. and I-Iiirnmei,le, IT,,Z . ~ M Z . C h e m , , 122, 202-9 ( I 941). (4) Sal-es, Y. R., Hnlr. Chim. A c t n . 2 7 , 942%; (1944). ( 5 ) Rees, H. I*.,and Anderson, D. H., -L~-.r., 2 1 , YS!j-O1 (1949 I , (6) Shriner, 1%.L., and Rcrger. Arthur, J . O r g . C h e m . , 6, 3306-18
(1941). R w m \ - b : c f n i re\-iew Augilzt 2 , Ig51.
Acrei7ted .January 5 , 1952.
Titration of Very Weak Acids with Lithium Aluminum Amides T 4 K E K C EIIGL-CHI, ,JESLS4 COSCEE4,
iVD
ROY KC'K-I\.IO'I'O
Srhool of Pharmacy, I'nirersity of Wisronsin, Madison, E i a .
'R
ICCESTLY it vias shown t h a t r.strenlely weak acids such as
:rlcohols, amines, and certain hydrocarbons could be detrrniined quantitative12 with lithium aluniinuni hydride as t h e reagent, (2-6). Iliguchi and Zuck ( 3 ) were able to titrate a n u m t w of these compounds with visual indicators using the h!.tlride as t h e base. Prrvious direct titrations of weak acids have h e m limited mainly to relatively strong acids such as phenols, rarhosylir acids, et(-., t h e strongest hase generally used * being of the alkoxide type ( 1 ) . Litliiuni :rluminum h)-dritie is not Liltogether satisfactory as the basic. reagent, because it may reart, Lvith reducible functional g r o u p such as aldehydr, ketone, ester, and other nonacidic groul)ings that may tie contained within t h e molecules. T h e prewnt investigation WNL: initiated t o test the feasibility of using lithium aluminum aniides as hases in t h e titratfon of extremely w t ~ t h :ncitls. It was hoped t h a t such h ~ s e sn-ould he capahlr of
reacting with hydroxyl groups hut ~ o u l dnot affectt such functional group^ a' carbonyl and cstei,, s.hic*h ai'e i,etlured hy t h e hydride. THEORY
For quantitative determination t h e conjugate arid of the base used for the titration must be considerahly weaker acid than t h e acid being titrated. T h u s it is possible to titlate niost mineral acids and c:irbosj-lir acids with hydi,osyl ions because water is a much ~ v e a k ~acid r than thew. I t is possihlr to titrate phenols with alkoxides because alcohols are much weaker acids. For titration of alcohols ant1 other acids of si~nilarstrength, a salt of an arid much weaker than alcohol is necessary. As most amines fall into this class, it is reasona1)le to expect that the nic~tallic. amidc. rould Iw used to titrate su1.h \veal< acids.
