BENZALDEHYDE I N ALMOND EXTRACTS.
1607
oleic acid gave in concentration of 2 0 0 parts per million practically the same results, very little transpiration, green weight about half of t h a t in the control solutions, and death of the plants in 1 2 or I j days. B V R E A UO F SOILS,
U.s. DEPARTMENT O F AGRICULTURE, W A S H I N G T O XD. , C.
THE COLORIMETRIC ESTIMATION OF BENZALDEHYDE IN ALMOND EXTRACTS. BY A. G . W O O D M AAN N D E. F LYFORD. Received August IO, 1908.
The recent successful application of the reaction with fuchsine-sulphurous acid to the colorimetric determination of acetaldehyde’ and of citral? suggested its similar use for the estimation of small amounts of benzaldehyde. Such il method would find immediate use in the assay of commercial almond extracts, for which the methods at present given in text-books are entirely inadequate, yielding results often 40 to j o per cent. too low. A procedure based on the colorimetric estimation has been worked out and is described in this paper,
Preparation of Reagents. Fuchszne-Sailplzurous Aczd.-o. j gram of pure fuchsine is dissolved in IOO cc. of water and a freshly prepared solution of sulphurous acid containing twenty grams of sulphur dioxide is added. When the solution is decolorized, sufficient water is added to make a liter. The amount of sulphur dioxide should be determined b y titration with iodine, or, if freshly prepared, its strength can be determined with sufficient accuracy from its specific gravity as found with a Westphal balance. A convenient method of preparing the solution is to balance the fuchsine solution on a scale pan and then to pass in a current of sulphur dioxide until the weight has increased by twenty grams. I n order to get a colorless solution, pure fuchsine should be used, and the solution can be relied upon for about ten days, the sulphuric acid formed by the oxidation of the sulphur dioxide decreasing its sensitiveness so much in t h a t time t h a t it is better t o use a fresh solution. This strength of sulphur dioxide was chosen after various experiments as giving less trouble in the use of alcohol containing traces of aldehyde, and being at the same time sufficiently sensitive. The difference in color produced b y 0.05 milligram of benzaldehyde is readily detected. It has been stated by Prud’homme3 t h a t benzaldehyde reacts b u t slightly with the ordinary fuchsine-aldehyde reagent and he has suggested Tolrnan, THISJOURNAL, 28, 1625. Ibid., 1472. Bull. sac. wad. Mulhouse, 74, 169.
1608
A . 13. TVOODJIAN .AND
E. F. 1,YFORD
a more sensitive form of tlic reagent, i i i \vhich sodium t hiosulpliate is used instead of sulphurotis acid ;IS t l i r tlccolorizitig agcnt. 'l'liis statement does n(1t agree hvith our e s ~ ~ c r i c ~i i~i c\vliicli c . tlic ~uclisiiie-sull,litir(~iis acid, . ;t tlistiiict clianjie iii c010r Jvitli o.c) j prepared as described a b o i ~ sho\\~etl The iiiotlified reagent proposed mg. beiizaldehytle i n a voluiiie (11' ~ C cc, I by I'rud'hoinnie did not give satisfactor!, results i i i o u r hands. 'I'he reagent was incon\-enient t o prepare, owing to the separation of finely divided sulphur, which could not lie removed by filtration. 'I'he reagent, furthermore, was too sensitive, giving a pink color ivhen standing for a few moments in contact with the air, even in the absence of aldehyde. .4Idehi,ife-~i,ce :~Icoizoi.-Coiisiderable attention was devoted to the preparation of this reagent. lye found it absolutely necessary to prepare it, although Yasey' says t h a t he n a s able to secure a coiiiiiiercial cologne spirit sufficiently free from aldehyde t o use. Suinerous experiments, the details of which need not be given here, were carried out to determine the most convenient method for preparing from commercial "cologne spirit" aii alcohol which should be free from aldehyde as shown by the Schifi reagent, made u p as described. Methods in\.olving oxidation of tlie aldehyde \\it11 sil\-er oxide were given thorough trial. IYinkler's method' as modified by L)unlap3 gave a n alcohol which showed cotisitlerahlt color \\it11 fuchsine-sulphurous acid, although the method was carried out esactlj. as prescribed. hndrews4 has recently described iii connection wit11 tlie determination of the refractive indices of alcohol-water mixtures a method for the preparation of pure alcohol, depending on treatment \villi quicklime and subsequent boiling with silver nitrate. T h e statement is made concerning the product t h a t "iio reaction for aldehydes could be obtained from it." In carrying out this method conimcrcial "cologne spirit \vas allowed to stand over quicklime, with frequent stirring, for four weeks. It was distilled twice from lime, collecting onl!. the middle portion each time, boiled for ten hours with silver nitrate and then allowed to stand four days over the silver nitrate. The middle portion of the distillate from the silver salt gave a decided color with the Schiff reagent. These oxidation methods with silver having failed in our hands to give satisfactory results, i t was determined to resort t o the methods involving the condensation of aldehyde with reagents to give non-volatile or difficultly soluble products. Of these the most promising appeared t o be meta-phenj-lenedianiine hydrochloride a s used by Tolman and by Chace in the work already mentioned. -1fter considerable work with this reagent "
.4nalysis of Potable Spirits. Ber., 38, 3612. THISJOURNAL, 28, 395. Ibid.,30, 353.
BENZALDEHYDE IN ALMOND EXTRACTS.
1609
we were enabled t o prepare by means of it alcohol which was absolutely free from color when tested for aldehyde by our reagent. I n order to secure a perfectly satisfactory alcohol, however, rather close adherence to certain details, which may be briefly mentioned here, is necessary. The meta-phenylenediamine reagent seems to remove only comparatively slight amounts of aldehyde, so t h a t it is essential t h a t the alcohol be relatively pure before being treated with the reagent. Hence commercial alcohol should first be treated with some preliminary reagent which will remove the greater portion of the aldehyde. Tolman, Chace and others have employed the customary treatment with caustic potash for this purpose, but we have secured much better results and in a far less time b y using the treatment with silver oxide, as suggested by Dunlap, as a preliminary step. Although i t is evident t h a t the greater part of the meta-phenylenediamine takes no part in the reaction, we have been unable to secure good results by using a less proportion than 2 j grams to the liter. Since this reagent is expensive, i t would render the process a costly one were i t not for the fact t h a t the greater part of the excess, being only difficultly soluble in 9 j per cent. alcohol, can be recovered unchanged at the end of the treatment. I t is probable t h a t if 3 to j grams of fresh reagent were added occasionally, j or 6 liters of purified alcohol might be obtained from 30 to 35 grams of reagent. From the slight solubility of the meta-phenylenediamine in alcohol, together with the very large excess t h a t i t is necessary to use, i t seemed probable that the reaction was very largely a question of the actual surface of reagent brought into contact with the alcohol. Such being the case, it seemed possible t h a t the only purpose served by boiling for several hours, as recommended by those who have previously used this reagent, is to keep the mixture of alcohol and reagent constantly stirred. Experiment confirmed this view and i t was found t h a t the same results could be obtained by shaking the reagent and alcohol in a shaking machine at room temperature as by boiling for the same length of time. Allowing the meta-phenylenediamine hydrochloride and alcohol to stand for several weeks with frequent shaking proved sufficient to give a fairly good grade of alcohol. The best results, however, were obtained by keeping the mixture stirred up for several hours by simply drawing a rather vigorous current of air through it. The method we have been using for some time may be summarized as follows, starting with commercial "cologne spirits : " 'l'his is first treated with silver oxide exactly as described by Dunlap' aiid distilled. '1'0 the distillate is added 2 5 grams of rneta-phenylenedianiine hydrochloride per liter and a fairly rapid current of air drawn
' L O G . Cit.
1610
A . C . \VOODX.iN
2'.Xl) 11. F. LYFORD.
through the solution for tlirce lioiirs. ' 1 ' 1 1 ~ ;rlcoliol is theii clistilled, the first 1oo cc. being rcjectetl. ,< J lie reiiiaintlcr oi the distillate should give at)solutel!. no color when tested for aldeli!-c!c i i i the iii;iiiiier clescrihed under tlic estimation of benzaldehydc, I t :vi11 reiiiaiii suitable lor use for several weeks at least, il' kept colt1 and iii the dark, preicr:il)l!, in an ice-chest. f ) c , 2 ~ , i . / , i i i i c i i i ~ oj ) ~ ! f { o m z l ( / v / ?lsiiC. - -1 staiitlartl solution o i beiiza1deli):de containing lor coiiveiiiciice
