Tetrachlorophthalic Anhydride, Acid, and Salts PROPERTIES AND SOLUBILITIES FRAXCIS E. L=IWLOR il'iagara Alkali Company, 'Yiagara Falls,.'?I
A discussion is presented of the properties and solubilities of tetrachlorophthalic anhydride, of the corresponding acid, and of some of its salts. The literature on the subject is reviewed and new- experimental data are submitted.
I n contrast to this, both the anhydride and the acid hemihydrate are completely stable under ordinary atmospheric conditions. Others have confirmed the fact that it is the hemihydrate vihich crystallizes from aqueous solutions ( I d ) . This hydrate of tutrachlorophthalic acid dissolves rapidly in wat,er t o form saturated solutions. The solubility of tetrachlorophthalic acid iyas determined at a variety of temperatures by titration with 0.1 *Vsodium hydroxide of a neighed portion of the saturated solution. The rwiilts (Table I and Figure 2 ) are a t variance with the values givcn ti>- Graehe. In the lower temperature range his higher results due to impurities are particularly noticeable. There is considerable difficulty in obtaining satisfactory data at teniperaturea approaching the boiling point because of the combined effect of high temperature coefficient of solubility and rapidity of evaporation of such solutions during the necessary manipulation of the samples. The solubility iricreaws rapidly near 100" C.; in order to determine vhether this trend continues beyond 100 C., several approximate determinations viere made by adding a known excess of tetraehlorophthalic acid to a suitable glass pressure flask and noting the t,emperature a t which all of the acid was dissolved. While the method is admit,t,edlyinaccurate, the experiment denionstrates that, the solubility continues t o increase rapidly with rise in temperature even above 100" C. (Figure 3).
G
R.4EBE first prepared tetrachlorophthalic acid and some of its salts in 1868 and made a preliminary s h d y of their
properties (4). Later when it had become commercially available as a dye intermediate, he studied it in more detail and prcpared many of it,s derivatives. These findings, published in 1887 (j), and the work of Delbridge in 1909 ( 2 ) , have served as the principal sources of information on this compound. Cnfortunately the product with which Graebe iyorked was not pure and was undoubtedly contaminated with loIyer chlorinated phthalic acid, iyliich led to erroneous resuks in the deterniinatiori of solubility and melting point. I n t,he course of the development of a process for the manufacture of this product it' became desirable to obtain more accurate data as well as to extend the field of inforriiation regarding this interesting compound. PROPERTIES
Gracbe gave the melting point of tetrachlorophthalic anhydride as 252" C. ( 5 ) . Delbridge carefully purified the conimercial product and obtained a compound melting a t 254.8255.2" C. ( 2 ) . Determinations of the melting point of sublimed tetrachlorophthalic anhydride by the heating and cooling curve method, as well as by the capillary tube method indicate a melting point of 254.9" i: 0.2" C. jvhich is in close agreement u-ith Delbridge's figure. Pure tetrachlorophtlialic anhydridr distills without appreciable decomposition a t a temperature of 366" C. a t 760 mn1. pressure. Boiling under reflux for several hours s h o w t h a t slondecomposition takes place and the neutralizatiou equivalent of the product decreases. This is probably the result of decarboxylation, as the aniouut of alkali-insoluble material iricreases with the period of boiling. The presence of various inorganic and organic impurities greatly accelerates the decomposition. The solid crystalline anhydride has a specific gravity of 1.92 a t 20" C. The liquid has a density of 1.52 grams per ml. at 275" C. Tetrachlorophthalic arihydride is insoluble or w r y slightly soluble in water, but hydrolyzes to the acid, slowly a t room temperature and more rapidly a t 100" C. (Figure 1). The solid crystallizing from the aqueous solution is the hemihydrate, C&14(COOH)2.*/,H~0. This point v e n t unnoticed by Graebcl a n d undoubtedly accounts for some of the errors in his analytical data. Delbridge discovered this fact and rioted t h a t the XT-atcrfree acid was rather difficult, t o prepare. It cannot be obtained by drying the hemihydrate in the usual way, but is obtained from the acid crystallized from dry acetone by driving off the acetone of crystallization. The pure acid is not stable as it absorbs nioisture from the atmosphere t o form the hemih>-drate.
1..
LL
l3
a0
Figure 1. LIydrol?-ais of Tetrachlorophthalic Anhydride in Water
_-_-Hours agitated
1 4
7 24 31 Before 95
1424
< i t 240
c,-----
Grams C6Clp(COOH)z formed/ 100 g s o h 0 0 0 0
A t 1000 c.----Grams CaCld(C0OH)z formed/
7---
Hours
03
agitated 2
06
4
1.74
09
8
2.74
27 0 34 0 37
100
g.
soln.
0.91
November 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
1425
TABLEI. SOLUBILITYOF TETRACHLOROPHTHALIC ACID IS KATER ASD
Temp.,
C.
IN
HYDROCHLORIC ACIDSOLUTIOM
Grains CsCla(COOH)z/ 100 G. Soln.
Grams
Temp.,
IN W A T E R 20 36 50 60
io
80
88 99
0.36 0.44 0.56 0.70 0.90 1 20 1.60 2.80
O
CaClr(CoOH)r/ C. 100 G . Soln. I N 0.1 S HCl 0.05 0.07 0.08 0.12 0.23 0.76 1.30
12 22 29 40 59 84 95
I r 0.6% HC1
PRESSURE A B O V E Ana.
50
The presence of a n inorganic acid exerts a depressing effect on the solubility of the acid in x-ater. The results in Table I and Figure 2 were obtained by titrating weighed portions of the saturated solution with 0.1 S sodium hydroxide and 0.1 S silver nitrate solutions to obtain the total acidity and chloride content, from which the amount of organic acid was easily calculated. The practical value of this effect is realized in the recovery of the acid from waste water in processes in which it is used.
Figure 2.
I
I
I
70
80
90
100
Solubility of Tetrachlorophthalic Acid in Water and i n Hydrochloric Acid
rand zinc salts were prepared, washed, and dried. T o determine their solubility in water portions of the saturated solution of the salt were subjected to analysis for the metal. Table 111, giving the solubilities of these salts, shows that the zinc salt is less soluble in hot than in cold water, a fact which was also observed by G r a e b ( 5 ) .
SOLUBILITY OF SALTS
The anhydride dissolves in alkali solutions to form the salts of the acid, which may be obtained even more readily by the reaction of the acid hydrate n i t h the alkali solution. The solubilities of the sodium and potassium salts were determined by evaporating to dryness a neighed portion of the saturated solution. The solubility of the sodium salt (Table I1 and Figure 4) increases rather rapidly with elevation of temperature up to 63.5 C.; above this point further temperature increase has little effect. The solid phase crystallizing out below 63.5” C. was analgzed and shown to be the pentahydrate, C6C14(COO?Ja)25H20. Analysis of ltrge, clear crystals formed by the sloiv atmospheric evaporation of saturated solutions at room teniperature showed t h a t they were also the pentahydrate. .kt temperatures above 63.5” C. the solid phase is probably not hydrated, but this point has not been proved.
60
ACID “DOUBLE SALTS”
Attempts t o prepare the sodium acid salt of tetrachlorophthalic acid resulted in the formation of a sparingly soluble acid “double salt” having the composition corresponding to the formula C6Cla(COOSa)(COOH).C6C14(COOH)1. The potassium acid “double salt” is completely analogous. These salts are similar in type to potassium tetraoxalate. When the theoretical amount of alkali hydroxide required to form the acid salt was added to a suspension of tetrachlorophthalic anhydride in water and heated to 100” C. with stirring, and just enough water added to bring the miterial into complete solution, a crop of crystals of the acid “double salt’’ separated on cooling. After filtration and evaporation of the filtrate, it was found to contain a relatively large quantity of the normal salt accompanied by some arid “double salt.” The reaction which probably took place may bc represented by the equation:
3C&ld(COONa) (COOH) --f C6Cla(COOSa)(COOH) . C&14(COOH)~ c & l a ( c o o ~ a , , T ~ B L E 11. SOLI-BILITYOF Son11 11TETR~CHLOROPHTHALATE IS KATER
+
Solubility of CsCL(C0OSa)z Sp. Gr. of Satd. Soln Grams/ T ~ ~ ~G . , ~ of~ CoClr(CO01\Ja)z ~ ~ / O C. 100 g. s o h . C. I00 g. s o h . Temp., * C. Sp. gr. 5.0 13.9 45.5 25.1 7 1.095 15.0 15.8 58.8 32.2 26 1.125 24.5 17.9 61.5 33.0 31 1.135 26.5 18.5 63..5O 34.0 77 1.188 34.0 20.8 75.0 34.6 37.5 22.4 97.0 35.2 40.0 23.0 a Transition point. Temp.,
-
The solubility of the potassium salt is sonieivhat greater than that of the sodium salt, but it has a loner temperature gradient so that the solubilities of t h r two salts are almost the same a t 6.5’ C. The solubility curve of the potassium salt s h o w no transition point in the interval 5-75’ C. (Table 111). The solid phase may be hydrated but loses n-ater so rapidly in the at’inosphere that it is difficult to determine definitely whether the solid is hydrated or has only adhering free water. When a solution containing the cations of a metal other than the alkali group is added to a neutral or slightly acid solution of a n alkali tetrachlorophthalate, the slightly soluble salt of the metal is precipitated. I n this manner the aluminum, calcium, cupric,
When a n inorganic acid, such as hydrochloric acid, is added to a solution of the normal salt, the acid “double salt” is precipi-
J 20
I
I
30
40
I 50
I
I
I
60
70
80
TEMPERATURE, ’C.
I 90
AI
I
I
00
110
120
Figure 3. Effect of Temperatures above 100” C. om Solubility of Tetrachlorophthalic Acid i n Water
z
Q4a
-
I-
to dissolve the anhydride in methyl, n-butyl, n-amyl, cyclohexyl, and tetrahydrofurfuryl alcohols. The dissolving rate is greatly accelerated by heating, but the resulting acid ester is also formed
'rhB1.E
z y 821 a
IT. SOLUBILITY O F TETR.~CIILOKOPHT€I.II.I(' .1IHYI)RIDE ORGASICSOLVESTS
IN
Soly. of CeClr(C0)20, Grams/100 G. Soln.
lx
Solvent Acetone Benzene
0
I
tated. This type of acid "double salt" of 4,5-dibromo- and 4,sdichlorophthalic acids n-as mentioned in the l i t e r a b e (6, I O ) . U S E S OF NOR\IAL SALTS
The, nornla~ ailver and sodium salts been uqed in rllc, preparation of the normal esters of tetraehlorop1ith:ilic acicl by reaction \,,.ith an appropriate organic halide (3, 5 , 7 , s;, Tile esters are not readily obtained by direct esterification (9, 1 4 ) ; therefore, this method may be of considerable import m c e especiallv in view of the ease wit,h lvhich the can be prepared, ~h~ normal salts ere propose,j for uee in treatment' of animal fibers to impart "wight" (18). Scandium was purified from the accompanying traces of and yttrium b y precipitation of the basic salt of tetrachlorophthalic acid ( 1 ) .
Temp.,
c.
25 25
Soly. 3.1 4.0
Temp.,
c.
49 76
Sol,.. 3 6 11 9
The hemihydrate, obtained by crystallizing t,he acid from water is very different from the anhydride, since it is freelv soluble in acetone, dioxane, and alcohol. I n contrast to the anliycliid[~,it is quite soluble in ether but is insoluble in benzene, carbon tet,racliloride, and nionochlorobenaene. HoJvever, upon addition of a sninil amount of methanol, it readily dissolves in t h r w solvonts and nlso in petroleum ether. I n view of these observations it is evident t h a t much of the information availablc in the 1itc.rature on the solubility of tetrachlorophthalic acid and anhydride is not reliable because the acid hemihydrate can be readily dritd t o form the anhydride; hence the solubilities refer to various mixtures of the acid and anhydride rather than to either pure acid or snhydride. The fact that only the anhvdride is soluble in benzene by nelbridge (a). ACKXOW L E D G l l ENT
TABLE 111. SOLUBILITY OF P O T A ~ ~ ASD I T XOTHERSALTSO F TETR.4CHLOROPHTHALIC . I C I D IZ \ y A T E R
SO~Y of. CsClc(C00X)z Temp., ' C. 7
14
20 23
22
10
Grams/ 100 g. s o h . 28.3 28.9 29 1 29 3 34 5 3; .5
801,. of Other Tetrachloroph thalates Tyw., G ra 111s / Salt C. 100 p. noln. .4lu1ninu iii 25 0 33 Calcium 24 0.O i Ciiiiric 25 a io Zinc 23 *-
2,;
iJ
The author wishes to acknowledge the assistance rendered by the Research Staff of the Niagara l l k a l i .Company, especially Gerald A. Thomas, Joseph L. Longo, and I. A. Hoekstra who carried out most of the analytical \vorlr in obtaining the data presented here. LITERATURE CITED
(11 Crookes, Win., Chem. .Yews, 102, 100 (1910). (2) Delbridge, T. G., Am. Chem. b.,41, 406 (1909). (3) Drake, N . L., and Sn-eeney, J . P., J . A m . Chem. Soc., 54, 2060 (1932). (4)
SOLUBILITY IN ORGANIC SOLVENTS
Table IT sllo\T-s the solubility (,E tetrac~llorophtha]ic arlhyti,,ide in sevcral .common organic solvents. Although no exact SolUbility figures are given for diorantx, it was found to solvent for the anhydride and dissolves 6-S5 at room temperature. An a t t e m p t xas made to determine the solubility of tetrachlorophthalic anhydride in ethyl alcohol at 20" C.; very large quantities dissolved, and finally a very sirupy liquid resulted. Drying a t 60" C. produced a crystalline materid which, by titration of an alcoholir: solution with 0.1 S sodium hydroside, gave a neutralization equivalent corresponding to the acid ethyl ester. Similar results were obtained when the attempt was made
bi.
the best
Graebe. C., Ann., 149, 18 (1868).
( 5 ) I b i d . , 238, 318-38 (1887). (6) IIolzinger, L., Rer., 74, 86-7 (1941). (7) L!-ons, E., and Reid, E. E., J , ~ 4 mChem. . S O c . , 39, li41 (Ig17). (8.1 Sle>.er. R., and Jugilewitsch, A , , R,er., 30, 784-7 (1897). (9) I.,, and ~ ~ d h ~ ~J.~J .u, Igb i dh. , , 27, 3146-53 (1894). (10) LIOIler, Julius, U. S. Dept. Coinmerce, Office of Puhlication Board, PB 625, p . 9 (Feb. 24,
1941). (11) Kite, R . V.. Jenkins, G . L., and ' Harden, TT'. C., J . Am. Chem. Soc., 59, 2000 (1937). (12) Scliwen, G . , and Krzikalla, H. (to I. G , Farhenind. A,-G.), U. 8 Patent 1,887,938 ( N o r . 15. 1932). (13) Teterin, Y, K., and Zonis, S. A.. J . Gen. Chem. (U.S.S.R.), 6, 65862 (1936). (14) Z a l ' k i n d . Y. S..and Belikova, M.. J . A p p l i e d Chem. (U.S.S.R.), 8 , 1210-13 (in German 1213) (1935). R E C E I V EJD u n e 4 , 1947. Presented before the Division of Organic Chemistry at the 111th IIeeting of the . ~ > l E R I C A . U C H E M I C A L SOCIETT. Atlantic City. S . J .
