T H E J O U R - V A L O F I N D U S T R I A L AATD E Y G I N E E R I Y G C H E M I S T R Y
1186
test as Expt. 11. Titration of IO-cc. portions of this acid required 2 5 . 7 2 and 2 j.80 cc. of sodium hydroxide; mean, 2 j . 7 6 cc. T h e first distillates from t h e xylene, on IO-cc. portions of t h e acid, required, respectively, 2 6 . 0 2 and 2 6 . 2 0 cc. of sodium hydroxide. After oxidation with permanganate, etc., t h e final distillates from phosphoric acid on aliquots equivalent t o two-thirds of t h e original acid taken neutralized, respectively, r 7 . o j and 1 7 . 2 5 cc. of t h e alkali. This proves t h a t propionic acid is completely recovered i n t h e method as outlined, and would be included in t h e final figures as acetic acid. EXPT. 6 - T a b l e I1 shows t h e difference, in cc. of standard approximately 0 . j A7 sodium hydroxide used and t h e corresponding quantity of acetic acid indicated, between t h e first distillate with xylene and t h e final distillate from phosphoric acid, on IO-cc. samples of pyroligneous acid from various retort runs. TABLE I1 Ouantitv of Acetic Acid Indicated G per Liter 70.81 70.02 73.32 72.38 84.65 59.53 $5.78 16.46 73.00 53.70 52.56 64.06
NaOH ..~~
No. 1 2 3 4 5 6 7 8
9 10 I1 12
Neutralized by First Distillate cc. 22.55 22.30 23.35 23.05 26.96 18.96 20.95 24.35 23.25 17.10 16.74 20.40
-
.
NaOH Neutralized by Final Distillate cc. 21.58 20.60 21.60 20.84 24.70 16.60 18.06 22.64 20.74 13.36 15.40 18.44
Actual Free Acetic Acid Present G per Liter 67.76 64.69 67.82 65.44 77.56 52.12 56.71 71.09 65.12 41.95 48,36 57.90
CONCLUSIONS
T h e accurate determination of t h e free acetic acid i n pyroligneous acid from pine-wood distillation cannot be made b y a simple titration, owing t o t h e fact t h a t t h e liquor turns black on addition of alkali and no end-point can be obtained, even when diluted 40 times. When it is distilled, directly or with steam, t h e same trouble is experienced with t h e distillate, on account of t h e large proportion of volatile phenolic bodies which pass over. A partial separation of t h e free acid from t h e impurities, affording a very close approximation of t h e free acetic acid present, can be made b y distilling t h e acid liquor with xylene. Even then foreign bodies of a n acid nature are present i n t h e distillate, and i n order t o get accurate results these impurities must be removed by a subsequent treatment of t h e distillate. This can be done b y oxidizing with potassium permanganate solution i n t h e presence of a small excess of alkali, with subsequent removal of t h e oxidation products. T h e close agreement between t h e results obtained i n t h e experiments and t h e theoretical quantity of sodium hydroxide solution required shows t h a t i t is p-ossible t o remove any acetone or methyl acetate from t h e first distillate, before treating with permanganate, by boiling t h e solution down several times, and t h a t t h e presence of pyrogallol or pyrocatechol, both of which, or bodies closely related thereto, may be prese n t i n pyroligneous acid, does not affect t h e final results. Richter’s “Organic Chemistry” states t h a t acetic acid is one of t h e products of t h e oxidation of pyrogallol i n alkaline solution. If such is actually t h e case, t h e acid, or its salts, must be produced in
Vol.
12,
So.
12
extremely small quantities, as indicated by t h e results obtained i n Expts. I1 and IV, and does not influence t h e final results. Formic acid is not included in t h e final results for acetic acid, since i t is completely oxidized t o carbon dioxide by t h e permanganate. Propionic acid would be unaffected, and included i n t h e final figures calculated as acetic acid. Butyric acid would probably be held back by t h e xylene on account of its high boiling point. THE DETERMINATION OF HYDROCHLORIC ACID AND NEUTRAL CHLORIDES IN LEATHER’ By Arthur W. Thomas and Alexander Frieden CHEMICAL LABORATORIES, COLUMBIAUNIVERSITY,N E W YORKC ~ r v
A method for t h e determination of sulfuric acid and neutral sulfates i n leather has been offered b y one of US.’ Briefly, this method is carried out as follows: One gram of leather is placed in a 250-cc. volumetric flask and covered with 2 0 0 cc. of a 0.1M KHgPOl (or NaHpPOn)solution. The flask is immersed in a bath of boiling water for 2 hrs. I t is then cooled, made up to the mark with water, shaken well, and filtered through a folded paper. The first 2 0 t o 25 cc. of filtrate are discarded, then 200 cc. of filtrate are collected, transferred to a 600-cc. beaker, 2 0 cc. of molar hydrochloric acid added, heated to boiling, and sulfate determined in t h e usual way by precipitation with barium ion. This procedure gives total sulfate. A second sample of leather is treated in a similar manner, except for the use of water instead of the phosphate solution, giving the neutral sulfate present. The difference between the two values obtained shows the amount of acid sulfate in the leather. It was undertaken t o apply t h e same principle t o t h e quantitative removal from, and determination of neutral and acid chlorides i n leather. MATERIALS E-Strap leather, vegetable tanned, treated with hydrochloric acid H-Vegetable tanned leather, treated with hydrochloric acid I-Vegetable tanned leather, treated with hydrochloric acid J-Vegetable tanned leather, treated with sodium choride K-Vegetable tanned leather, treated with sodium chloride M-Chrome calf leather, treated with hydrochloric acid S-Hide powder, tanned with chromic chloride
Leathers H, I, and M were prepared b y soaking finished samples of t h e cut-up leathers i n dilute hydrochloric acid, after which t h e y were filtered, washed just enough t o remove adhering acid solution, and dried. Leathers J and K were prepared in a similar manner, using sodium chloride instead of hydrochloric acid. E X P E R I M E N T A L PART EXTRACTION WITH PHOSPHATE soLuTIos-Experiments were carried o u t t o note t h e effect of different times of heating and of different weights of leathers on t h e extraction of t o t a l chlorides by t h e phosphate solution. The reason for trying different weights was due t o t h e fact t h a t in t h e case of sulfate extraction it was found t h a t not more t h a n I e. of leather containing more t h a n j per cent,SOa could be used, if a quantitative removal of t h e sulfates was t o be accomplished by use of 2 0 0 cc. of t h e phosphate solution. 1 Presented before t h e Leather Chemistry Section a t the 60th Meeting of the American Chemical Society, Chicago, I l l , September 6 t o 10, 1920. 2 A W Thomas, J A m Leafhev Chem Assoc., 16 (19201, 504.
Dec., rgzo
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
As shown below, 2 hrs. were found sufficient time for t h e digestion and I-g. samples not too large for quantitative results. Extraction times longer t h a n z hrs. did not yield any more chloride t h a n t h e 2-hr. extraction. Leather N Grams 0.5 1.0 2.0
Chloride, Calculated as C1, Extracted by 0.1 M KH2PO4 Solution in 1 Hr. 2 Hrs. Mg. Mg. 39.6 .... 41.1 39.5 39.8 37.3
E X I R A C T I O N WITH wATER-Since neutral sulfates are quantitatively extracted from leather b y means of pure water in z hrs. at I O O O C., this procedure mas tried upon t h e samples of leather containing sodium chloride, with t h e following result:
I,EATHER
CI Found KHIPOa Extraction Mg.
C1 Found Water Extraction Mg. 17.8 23.6
LEATHER H 11 N
40.1
chloride is much more readily hydrolyzed t h a n collagen sulfate. EXTRACTION WITH ALcoHoL-Since hydrolysis of t h e collagen-acid compound cannot take place in alcohol, while chlorides are soluble in this solvent, its efficacy for extraction of neutral chloride was studied. The 9j per cent ethyl alcohol was purified by distillation over alkali. The typical figures given below show t h a t alcohol quantitatively removes neutral chloride from leather. The digestion was carried out a t 75' C. for 2 hrs., although in many cases 1.5 hrs. were found t o be sufficient.
LEATHER
Neutral C1 Present per Gram Sample Mg. 17.8 23.7
C1 Extracted by Alcohol per Gram Sample Mg.
17.9 23.6
'
Hence, in t h e case of these leathers which contained neutral chloride only, all t h e chloride was extracted with water, because, as will be shown later, these yields are identical with those obtained b y phosphate extraction which removes all chlorides quantitatively. I n the sulfuric acid method it was found t h a t while all t h e neutral sulfate was removed by digestion in water a small portion ( 7 t o I O per cent of t h e total) of t h e acid sulfate was hydrolyzed and extracted as well, and. therefore, t h e effect of water on t h e acid chloride was investigated with t h e result: Total Acid CI Present per Gram Mg. 19 9 28.1
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Scid C1 per Cram Extracted by Water in 0.5-Hr Digestion Mg 19 5 16 9 17 1
I t was obvious from these experiments, t h a t t h e water extraction could not be used for separation of neutral chloride from acid chloride in leather. Sample H showed practically complete removal of t h e hydrochloric. acid b y wat9r. This effect has been noted b y us in other samples of vegetable tanned leathers which h a d been treated with hydrochloric acid, and we do not consider such prepared samples as proper material upon which t o base a test. It appears t h a t all of t h e hydrochloric acid does not combine chemically with finished iregetable tanned leathers, because it reacts with the same groups of t h e collagen molecule as tannins do. I n t h e cases of chrome tanned samples, M and S . all t h e acid chloride was not extracted b y water, but since t h e amount removed was so large, it was evident t h a t t h e method which worked very well for sulfuric acid and neutral sulfate separation would have t o be modified if separation of acid and neutral chloride was t o be attained. Since, in our opinion, acids are chemically combined with collagen, provided they come in contact with t h e collagen before all t h e reactive groups of t h e collagen are combined with tanning agents, t h e removal of a n acid from leather by means of hot water is due t o hydrolysis. It is evident then t h a t collagen hydro-
The amounts of acid chloride extracted b y alcohol after z hrs. digestion a t 7 5 ' C. were as follows: LEATHER I
L PI7
Acid C1*Present per Gram Sample Mg. 21.1 28.1 40.1
Acid CI' Extracted by Alcohol per Gram Sample Mg. 5.4
5.4 5.9 1 While we call this "acid chloride," we have no means of knowing whether all is present as such. The leathers in the cases of I and I,, and the hide substance in the case of K were treated with acid chloride solutions, but this treatment does not necessarily result in its all existing in the leather as acid chloride, since it is quite possible t h a t some may have been converted to neutral chloride in the leather.
The above experiments indicated t h a t while neutral chloride was quantitatively extracted by alcohol, a small amount of t h e acid chloride present was apparently extracted as well, but on account of t h e possibility t h a t some of the chloride considered as acid chloride might have been converted t o neutral chloride, and alsc since no method for t h e determination of hydrochloric acid in leather is available, we feel justified in offering this as a satisfactory method a t the present time. MET H 0 D T O T A L cHLoRmE-One gram of leather is placed in a zjo-cc. volumetric flask and covered with zoo cc. of a 0.1 M solution of KH2P04 or N a H s P 0 4 . The flask is immersed in a bath of boiling water for z hrs., and shaken occasionally. The solution is then cooled, made up t o t h e mark with water, shaken well, and filtered through a folded paper. The first 20 t o 2 5 cc. of filtrate are discarded, then zoo cc. of t h e filtrate are collected in a volumetric flask, transferred t o a 600-cc. beaker, and acidified by addition of I O cc. of molar nitric acid which prevents precipitation of silver phosphate when t h e silver nitrate is added later. The solution is heated and I O cc. of 0.1 M silver nitrate solution added. After t h e silver nitrate treatment, a further addition of 20 cc. of concentrated nitric acid ( I j M ) is made, and this mixture is evap@rated in the dark t o about j o cc. volume, in order t o oxidize and dissolve organic matter which has precipitated with and contaminated t h e silver chloride. The solution is then diluted with about zoo cc. of water, heated, and filtered through a Gooch crucible. The silver chloride is washed, dried, and weighed in the usual manner, and the total chloride in t h e leather
