11;z
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
I n the work on t h e resistance of leather t o washing, we tanned five portions of hide powder with each sample of tanning material examined, of which three were washed immediately after tanning and two dried without washing. After thirty days the washing of one of these powders from each set was begun. After t h e twentyfifth washing it was dried and analyzed for comparison with the powders washed immediately after t a n ning. The results in Table VI1 show a distinct increase in tannin due t o aging. I t is intended t o keep the fifth powder of each set for a full year before washing. S U I T A B I L I T Y O F T H E N E W METHOD AS A S T A K D A R D
We believe t h a t t h e experimental d a t a in this and t h e earlier paper prove not only t h a t t h e new method is correct, but t h a t t h e A. L. C. A. method, and, therefore, also the official methods of Europe, are greatly in error. I n actual practice we found barely 50 per cent as much tannin in t h e leather coming from a certain upper leather yard during a 3-yr. period as was p u t into it, according t o t h e analysis by the A. L. C. A. method of the extracts used. On the other hand, t h e new method now checks this yard easily within t h e limits of experimental error. We feel justified in recommending t h a t t h e new method, or some modification of it, be adopted as a standard t o replace the present official methods. It has been contended, and perhaps rightly, t h a t the new method is so time-consuming as t o make it unpopular for routine work, but i t should be realized t h a t no serious effort has yet been made t o simplify the method, all work u p t o t h e present having been confined almost exclusively t o t h e question of correctness. One modification t h a t appears promising for routine control work is t o t a n the hide powder as usual, transfer it t o a n alundum thimble, wash i t by means of a mechanical arrangement, and then dry a n d weigh it, the increase in weight of the dry hide powder being taken as tannin. No doubt other modifications will suggest themselves as t h e work proceeds, but the saving of time is not sufficient compensation for the errors involved in the official methods. SUMMARY
Tannin once combined with hide cannot be removed t o an appr,eciable extent by any amount of washing t h a t would be practical. It has been discovered t h a t chemical changes are produced in a t a n liquor by boiling or evaporating, whereby certain non-tannins are converted into substances capable of tanning. Such changes can be followed quantitatively by means of the authors’ new method for tannin anal’ysis, but not by t h e official method of the American Leather Chemists’ Association. The new method can also be used t o study t h e “aging” of leather. T h e new method gives results which agree closely with tanning practice, whereas t h e A. L. C. A. method was found t o be greatly in error. It is recommended t h a t the new method be adopted as a standard.
Vol.
12,
No.
12
THE THERMAL DECOMPOSITION OF TURPENTINE WITH PARTICULAR REFERENCE TO THE PRODUCTION OF TOLUENE AND ISOPRENE By S. A. Mahood FOREST PRODUCTS LABORATORY,
MADISON,
WISCONSIN
Received August 21, 1920
The decomposition of turpentine by heat was first investigated by Berthelotl and later by Hlasiwetz,z Schultz,3 and TildenS4 Hlasiwetz passed turpentine vapors through a red-hot iron tube filled with porcelain, and obtained a liquid which had t h e odor of benzene, and from which was obtained on distillation a fraction which began t o boil a t 30’. Schultz, using an iron tube heated t o dull redness, obtained a liquid which contained benzene, toluene, xylene, unchanged turpentine, naphthalene, phenanthrene, anthracene, and methylanthracene. Large quantities of combustible gas were also formed during the heating, Tilden showed the low boiling product obtained by Hlasiwetz t o be identical with isoprene obtained by Williamss by t h e distillation of India rubber, He also showed t h a t t h e difference between the results obtained by Hlasiwetz and Schultz was due t o a difference in t h e temperature of t h e tube through which t h e vapors were passed. The discovery by Tilden6 t h a t isoprene polymerizes t o India rubber has led t o considerable experimental work on t h e production of isoprene from the terpenes. Aside from the patent literature, however, t h e yields reported have in t h e main been too low for practical purposes. Harries’ obtained I per cent of isoprene from commercial pinene, using his isoprene lamp. Herty and Grahams obtained 5.5 per cent (by volume) of isoprene from turpentine, and 8 per cent from a fraction boiling between I j 5 ’ and 1j6’. Using commerciallimonene, Harries obtained a yield of 30 t o 50 per cent of isoprene, while Herty and Graham obtained 1 2 per cent from a limonene fraction. Staudinger and Kleverg obtained a yield of 60 per cent of isoprene from limonene by working a t a pressure of 4 mm. According t o patents issued t o Schering and Company,1° larger yields of isoprene are obtained from @-pinene t h a n from a-pinene, but Schorger and Sayre“ found t h a t these two terpenes give approximately t h e same amount of isoprene when passed through t h e same apparatus for purposes of comparison, the yields obtained by them being approximately I O per cent. Several patents have been taken out covering the production of isoprene from turpentine. Woltereck12 passes the vapors of turpentine through an iron tube filled with contact material such as wire gauze, perforated disks, or similar material. The optimum temperature for t h e production of isoprene is said t o be Ann c h i n phys. 131, 39, 5. B e y . , 9 (1876), 1991; Z C h e m . [2], 4, 380 3 Bey., 10 (1877), 113. 4 J . Chem. S a c , 45 (1884), 410,Chem Newy, 46 (1882), 120 5 Tyans. R a y . Sac. London, 1860, 241. 8 Chem News, 66 (1892), 265. 7 A n n , 383 (1911), 228. 8 THIS JOURNAL, 6 (1914), 803. 9 Bev., 44 (1911). 2212 10 D.R P. 260,934;U. S. Patent 1,057,680. 11 THISJOURNAL, 11 (1915), 924. 12 Brit Patent 27,908 (1909). 1
2
Dec.. 1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY Tnam I Ternper=-
IS*
prene FVAC.
*"le
RUX NO. 6 7 8
.
" c.
Contents Of
Tube
0
16
I1
12 13 t4
I5 22 23 24 25 26 27-31 32 33
34
3 M O
45 46 47-533 I
@.;
120C. 156205 450 156200 500 155-200 550 155-200 600 155-200 650 155-200 700 600 154-200 155-159 6W 600 155-2W 152-235 600 157-200 350 400 157-200 450 155-210 157-190 5w 157-165 550
5w 300 400 400
5w
36 37 38
I
Tube
450
35
f
Time
of Fraction Taken
Smell piece9 of Unglared porcelain were uaed Average. Total quantities for seven runs are given
550' C., unless the vapors are diluted with an inert gas such as nitrogen, when a temperature of 600' C. is required. Heinemann' passed turpentine vapors over finely divided and heated copper or silver, or through a heated structure of these metals. With copper a temperature of about 48o0 C. is required, while with silver the optimum temperature is about 450' C. No figures on the yields are given. If the vapor is diluted with steam and the temperature of the tube raised t o ? S O 0 C. a yield of 40 to 50 per cenf of the material used is said to he obtained in the form of hydrocarbons boiling below I O O O C., two-thirds of which is isoprene.2 Gross3 claims to have obtained increased yields o[ isoprene by "cracking" turpentine in the presence of metals, metallic oxides, or mixtures of oxides and chlorides as catalysts at temperatures of 264' t o 700" C. With copper oxide the effect is said t o be apparent at 2 6 0 ~C. and is maximum at 3 0 5 ~C., when a yield of 35 per cent of isoprene is obtained. With copper as a catalyst, soo' C. is the optimum temperature, and a yield of 17.5 per cent is obtained. From an examination of the literature it is apparent t h a t data on the variation of the percentages of dit{erent products formed with change in temperature by "cracking" turpentine are rather meager, and that in.most of the work no record of temperature has bee? made. The present work was undertaken for the purpose of investigating this variation, particularly with reference to the yields of isoprene and toluene, since the dibromide of the former has promise of being a suitable lachrymatory gas and the latter is needed in increasing quantities for the manufacture of the high explosive, trinitrotoluene.' *Brit. Patents 14.W aod 24.236 (19101. *Brit. Patent 1953 (1912). I U. S. Patent 1,099,498. 4 The work reponed in this p a p r wm b e a n in October LPI?.
1x53
.....
157-185 157-200 160-220 158-210
tion Of up to Run 50°C.
G. 0
zits.
3.75 3.50 3.50 3.00 3.50 2.50 3.25 3.25 2.75 2.50 2.50
6
17 47 42
64
1.25
40 50 19 0 0 7
1.W
50 54
m
1.25 1.25
.....
1.50
6 3 11 22 34
1.00 1.50 2.50
156210 2.w 550 2.50 48 155-215 600 .. 6504 47.7 2.75 .. 134.3 I8 450 160-205 145.0 17.1 38.8 157-180 2.75 500 14.33 6ji.9 1628.6 8.7 370.3 450 .157-2W * Csrboniratiao caused the tube to become plugged. S Iroo tube.
.....
......
1.5 0.75 ?1 0.9 0 . 5 {?I 139.4 4.98'
EXPERIXENTAL'
The type of apparatus used throughout the work is shown in Fig. I . In Runs I t o 44, inclusive, t h e heating unit consisted of a pyrex glass tube 26 mm. in diameter and wrapped for one meter of its length with 24 B and S gage nichrome wire, In all subsequent runs an iron tube of the same dimensions and similarly wrapped was used. The water in the Hopkins condenser was maintained at 50' C., so that the low boiling products passed through this condenser, and were subsequently cooled in the spiral condenser, and a spiral glass tube surrounded by a freezing mixture,
Fto. I
and collected in a series of three receivers, one of which contained carbon tetrachloride, cooled in a freesing mixture, The high boiling products were condensed in the Napkins and allowed to ru4 hack as desired, ........ to the distillinp flask or traaDed -. Two hundred grams of turpentine were used in each run. ~
L A h o w k d g m e n t b made to Messrr. R
for e d s t m c c io this work.
E. Kremers and D. E. Ceble
1154
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
Temperature "C. FIG.2
The isoprene fraction was immediately distilled through a I 2-in. Hempel column containing glass beads, and the portion boiling between 30" and 40" was taken as isoprene, since practically all of this portion on redistillation boiled between 3 5 " and 3 7 ". No attempt was made t o determine t h e amount of trimethylethylene t h a t may have been present in t h e isoprene. The results of some typical series of runs are given in Table I. I n Runs 6 t o 1 1 the-vapors were passed through t h e tube repeatedly, t h e high boiling distillate being allowed t o return t o t h e distilling flask. It was observed, however, t h a t decreasing amounts of low boiling products were formed as t h e distillation proceeded. Subsequently it was shown (Runs 14 and 15) by passing t h e vapors through t h e heated tube once and then passing t h e distillate boiling a t more than j o o through the tube again, t h a t all of the isoprene obtained is formed during a single passage of the vapors through the tube. Accordingly, in all subsequent runs recorded in this table, t h e vapors were passed through the tube but once. With an e m p t y glass tube a maximum yield of isoprene is obtained a t 600°, while with the same tube filled with porcelain 500' appears t o be the optimum
Vol.
12,
No.
12
temperature. With the tube filled with a mixture of copper oxide and copper chloride prepared according t o t h e patent issued t o Gross,l no effect whatever i n increasing the yield. of isoprene was apparent. Using an iron tube containing no contact material, the most suitable temperature for the production of isoprene appears t o be 450". According t o Harries,' t h e production of isoprene from turpentine is due t o t h e presence of limonene (dipentene) in the turpentine. Wood turpentine, which contains considerable l i m ~ n e n e ,might ~ therefore be expected t o give a larger yield of isoprene t h a n gum turpentine. Results obtained in Runs 1 2 and 13 do not, however, confirm this. The high boiling distillate and t h a t portion of t h e isoprene distillate boiling above 40" were fractionated twice, using a 12-in. Hempel column filled with glass beads. The results obtained with the distillate secured in Runs 2 2 t o 2 6 are typical, and are given in the form of curves in Fig. 2. Complete analyses of the various fractions were not made, but qualitative tests showed considerable quantities of terpenes in the higher boiling fractions obtained inc"cracking" a t the lower temperatures, while hydrocarbons of t h e benzene series and olefinic hydrocarbons are t h e chief constituents of all fractions a t "cracking" temperatures over 400". The yields of the fractions boiling under 1 2 5 " C. reach a maximum a t 500°, as does the residue remaining a t ISO", while t h e fraction boiling a t 12 j" t o I j o o and t h e gas formed during the "cracking" process continue t o increase with increase in the cracking temperature. By means of its 2,4-dinitro compound3 (m. p. 70" t o 71"), toluene was found t o be a chief constituent of t h e fraction boiling a t 100" t o I 2 j O . The fraction boiling between 125' and 150" when tested for mxylene gave a trinitro derivative melting a t 1 7j " t o 176". The melting point of pure trinitroxylene is 181" t o 181.;". The acid obtained by oxidizing a portion of the fraction boiling between 165" and 180' gave a dimethyl ester melting a t 138". Cymene under the conditions of t h e test gives dimethyl terephthalate which melts a t 140". T h e fraction boiling a t 150' t o 16;" upon similar treatment gave a dimethyl ester melting a t 5 5 ' (dimethyl isophthalate melts a t 6 4 O ) , indicating m-xylene and probably other m-compounds of the benzene series as constituents of this fraction. The gas formed has a n odor somewhat similar t o $hat of coal gas and burns with a luminous flame. When placed in contact with fuming sulfuric acid, I O t o 2 2 . ; per cent by volume dissolves, showing olefines present t o t h a t extent. Since, according t o the literature, larger yields of isoprene appear t o be obtainable from limonene t h a n from other terpenes, experiments were carried out in which turpentine was treated so as t o convert t h e pinene into limonene before "cracking." According t o 1 LOC. 9
a
cit.
Forest Service, Bulletin 106 (1913). Mulliken, "Identification of Pure Organic Compounds,'' 1 (1908), 202.
