DUNNINGHAM : THREE COMPONENT SYSTEM, ETC. 431

L1II.-An Exact Investigation of the Three Corn,- ponent System : Sodium Oxide, Acetic Anhydride, Water.

By ALFRED CHARLES DUNNINGHAM.

THIS system has already been investigated a t 30° by Dukelski (Zei t sch . m r g , Chem., 1909, 62, 114), who gave the following as the phases stable at that temperature : C,H,O,Na,&H,O; CzE30,Na,3Hz0 ; C2H3O,Na,C&H4O2 ; and C2H30&Ia,2C2H,0,.

The research deacribed below wa-s undertaken for the following reasons :

(1) It appeared improbable that a hydrated salt should exist at 30° in contact with a concentrated solution of sodium hydroxide, especially as anhydrous sodium acetate is not deliquescent. Accord- ing to Dukelski, however, the hemihydrate can exist in contact with a saturated solution of sodium hydroxide.

(2) The system appeared of especial interest, because, according to the same author, the saturation curve of the acid salt, C,H3O&a,C2H40,, is divided into two parts, separated by the saturation curve of the acid salt, C,H,0&Js,2C&H40e. This means

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482 DUNNINGHAM : THREE COMPO(NEWT SYSTEM :

that there are two distinct saturated solutions, in contact with which the campounds CiH,O,Na,C,H,O2 and C2H,02Ne,2C,H40, can exist in equilibrium a t constant temperature, and it would appear that the addition of either water or acetic anhydride to a solution of sodium acetate in pure acetic acid tends merely to dilute the acid and bring about the formation of the s d t containing only one molecule of acetic acid.

The system has been completely investigated a t Oo, 15O, 30°, 4 6 O ,

FIG. 1.

00.

F= NaOH,CH,O. d =C,H,O,Ns. B= C,H,O,Na,3H,O. C=C,H,O,Na,G,H,O,. D=C,H,0,Na,2C1H40, E=0,H40,.

60°, and 7 5 O , and partly a t 5 O and 20°. The temperature never varied more than O*Io during any experiment.

The nature of the solid phase has been determined by Schreine- makers' midue method (Zcitsch. phgsikal. Chem., 1892, 9, 57), in which both the solution and the wet solid (the residue) in contact with it are analysed. The two p o h h obtained by plotting the compositions of the solution and residue respectively should lie in a straight line with the point representing the wmpmition of the pure eolid phase.

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SODIUM OXIDE, ACETIC ANHYDRIDE, WATER, 433

Other experimental evidence has been used when necessary. The appearance of the solid phase is generally a clear indication

of its nature, since all the compounds have a definite crystalline form, &9 follows:

C,HI,O,Na = scaly plates. U,H,0,Na,3H20 = rhombic prisme. C,H,O2Na,C2I€,O, = rectangular prisms. C,H,02Na,2C,H,0, = fine needles.

FIQ. 2.

1 5 O .

Percentage of (CH,’CO),O. O= NaOH,31H20. A =C2H,0,Na. B = C2H8O2Na,3H,O. C=C,H,O,Na,C,H,O,.

D=0;H,02Na,2C,0,0, E= C,H,O,.

The samples were andysed in such a way that the free acid or alkali wa8 titrated, whilst the sodium was estimated aa chloride, a duplicate analysis being made in each case.

All data concerning the compounds of sodium oxide and water are taken from Pickering’s figures (Trans., 1893, 63,890).

The isotherms obtained are shown diagrammatically in Figs. 1 to 6. I n these figures all possible mixtures of sodium aeetate and water lie on the line 08. All mixtures of solid and eolutian, or solutions, on the left of 08 are allreline, and all those on the right

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434 DUNNlNQHAM : THREE COMPONENT SYSTEM :

of it are acid. All mixtures of sodium acetate and acetic acid lie on the line AE, whilst to the right of this lie all mixtures contain- ing free acetic anhydride. Between 08 and A E lie all mixtures of sodium acetate, acetic acid, and water.

A t 00 (Fig. 1) the solubility of the compound NaOH,4H20 is only slightly affected by the presencz of the compound

C 2 H , 0 2 N a , 3 ~ 0 to saturation; b representij a solution saturated with respect to C,H,02Na,3H20 and NaOH,4H20 ; C2H,02Na,3H20 is the stable phase over the long range of concentrations represented by the line bd, extending well into the acid portion of the diagram. bd is the saturation cuwe of C$H,02Na,3&0 in all the figures.

A t the concentration corresponding with d, a new phase, C,H,02Na,C2H,02, appears, which, however, has only a small range of concentrations over which it is stable. A t e, C2H,O,Na,2C~,O2 appears, and remains as the stable phase up to pure acetic anhydride, except where the curve is intersected by the freezing curve of acetic acid, rpqt.

A t the extreme right of the curve, C2H,02Na must have a small range of saturations for the reason pointed oat by Schreinemakers (Roozeboom, Heterogene Gleichgewichte,” III., 1911 edition, p. 208). A t Oo acetic acid itself has a saturation curve, represented by rppt, and this curve cute the saturation curve of

( e f ) in p and q. Attempts to obtain supersaturated solutions of C2ElsO$Ta,2C&H402 between p and q have been Unsuccessful, the solution forming a mixture of acetic acid and C2Hs02Na,2C2H,02, plus the saturated aolution p , or a mixture of acetic acid aad C2H,0,Na,2C2H402, plus the saturated solution p.

A t 15O (Fig. 2) anhydrous sodium acetate appears, in contact with a small range of solutions, represented by the line ab, and we have the following saturation curves :

C2HS0aa,2C2H402

bo? corresponding with C2H,0,Na,3H,0 ds $ 9 $ 9 C2H802Na,C2H402

c f $ 9 3, C$@2Na,2C,H40,- The isotherm at 30° (Fig. 3) is of particular interest because

the author has been unable to confirm the results of Dukelski (Zoc. cit.). According to that author, C2H,0aa,3H20 is dehydrated by sodium hydroxide, giving C&H,02Na,&H20. Further, Dukelski states that C2H,0,Na,C&H402 has a second saturation curve. Special attention has been devoted to these points :

(1) The dehydmtion of C2Hs0aa,3&0. The residue method shows that C2H,02Na is undoubtedly the

solid phaee produced by the dehydration. C&H,02Na,3H,0 melte

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SODIUM OXIDE, ACETIC ANHYDRIDE, WATER. 43 5

a t the same temperature alone or mixed with anhydrous sodium acetate.

(2) The recurrence of ~H,0zNa,C,H40, in stronger acid solution8.

Both the residue method and the appearance of the solid phase point to the uninterrupted existence of CaH,0,Na,2~H40, in high concentrations of acetic anhydride. As already mentioned, C,H30,Na,C,H40, separates out in prisms, and CzH,O&Va,2C,H4Oz

FIQ. 3.

30'.

in needles. A t higher temperatures, where a recurrence of the CzH,0zNa,C,H40, curve waa obtained, the prisms were unmistak- able. The solid phase in solutions of acetic anhydride at 30° waa dried, and its composition and melting point were practically identical with those of CzH,0zNa,2C,H40,. Dukelski did not determine the composition of solutions saturated with respect to two solid phases, and the isotherm plotted from his figures and shown in dotted lines in Fig. 3 differs materially from that obtained by the author.

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436 DUNNINGHAM : THREE COMPONENT SYSTEM :

A t 4 5 O (Fig. 4) the field of CzH,0&7a,3&0 is rapidly narrowing, for the transition temperature of C,H,0zNa,3Hz0 and GH,OzNa in the two component system is 5 8 O . CzH,OzNa,CzH,O, has now two saturation curves, de and fg, separated by ef , the saturation curve

This exists only in the region of solutione containing a maximum quantity of acetic acid, and there are two saturated solutions,

of $HsO,Na,2Cz&Oz.

FIG, 4. 450.

Percentage of itCH8'CO),O. E=NaOH,lH,O. A = C,H,O,Na. B= C,HsOli'?a,3H,0. C= C,H,0,Na,C2H,0,.

D= C,H,0,Na,2C,H,01. E= CQH,Oa.

e and f , in contact with which CzH,OZNa,CzHH,O2 and CzH,0,Na,2CzH,0,

can exist simultaneously. The composition of the former solution can be expressed in terms of sodium acetate, acetic acid, and water, and that of the latter in terms of sodium acetate, acetic acid, and acetic anhydride.

A t 60° (Fig. 5) CzH,0zNa,3&0 can no longer exist, aince it melts alone a t 5 8 O . CzH,OZNa,~H,Oz and CzHsOzNa can now, therefore, exist together in contact with the solution represented by b (or d) . This point lies on the neutral line AO, and the

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SODIUM OXIDE, ACETIC ANHYDRIDE, WATER, 437

addition of acid to a saturahd solution of C,H,O,Na in water causes immediate separation of C2H302Na,C2H40,. The latter compound still has two saturation curves, de and fg, separated by the curve ef corresponding with saturated solutions of GH,02Na,2C2H402, and there are two saturated solutions in contact with which C2H,02Na,C&€402 and C2H,02Na,2C,H,02 can exist together. One of these, e, may be represented in terms of

FIQ. 6.

60'.

Percentage of (CH,'CO),O.

H= NaOH, 1H,O. A =C,H,O,Na. C= C,H,O,NR,C,H,O, D=C,H8O,Ne,2C,H,O,. E=C,H,O,.

sodium acetate, acetic acid, and water; the other, f, in terms of sodium acetate, acetic acid, and acetic anhydride.

At 7 5 O (Fig. 6) we have only t w o phases containing acetic anhydride, namely, GH,O,Na, represented by ab(ad), and C2H,02Na,C2H,0,, reprwented by d g ( b g ) .

The space model in which all these isotherms are plotted against the temperature is shown diagrammatically in Fig. 7.

Adjoining the fields of NaOH, NaOH,lH,O, NaOH,2Hz0, and NaOH,3iHz0 is the field in which the anhydrous salt, C2H,02Na, is stable. This field is bounded on the right by the field of

VOL CI. Q C ?

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438 DUNNINOHAM : TBREE COMPONENT SP STEM :

C2H,OZNa,3&O, which ends a t the point P (68O), the melting point of CYZH30ZNa,3Hz0 in the two component system, sodium acetate-water. Above the point I' the field of CZH30ZNa is bounded by the neutral line, beyond which C2H3OZNa,C2H,Oz exisb. In no case could a field of saturation of C2H,0,Na,&HZ0 be observed, which, if it exists, must be formed from the trihydrate before the anhydrous salt, and must have a field lying between

FIG 6.

76O.

Percentage of (CH,'CO),O. K= NaOH. A = C,H,O,Na. C= C,H,O,Na,C,H,O2. E= C,H,02.

the fields of these other compounds, namely, C 2 H 3 0 a a and

Also, if there is a hemihydrate, the addition of a saturated solution of C*,H80&a,3&o at 50° to a quantity of anhydrous salt should cause a rise of temperature to the transition temperature of CZH3O2Na,~HzO and C;2H3OZNa, and the addition of a large quantity of anhydrous salt to the half-melted mass a t P should cause a temperature change. This is, however, not the caae.

The lowest temperature at which C2H,0zNa,3Hz0 is dehydrated

CzH,OzNa,3H,O.

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SODIUM OXIDE, ACETIC ANHYDRIDE, WATER. 439

At this transition point R, a satur- by sodium hydroxide is 11’2O. ated solution of sodium hydroxide can exist with solid

and the anhydrous salt. C,H302Na,3H,0

The compound C2H30,Na,2C&140, melts a t 74.8O, giving

Percentage of N%O.

C,H302Na,C,H40, and acetic acid. Since its maximum stability is in the two component system C,H,O,Na-C,H,O,, the limit of its field is a t the point X, where the saturation curve at 7 4 . F is cut by the line AE, on which lie all mixtures of acetic acid and sodium acetate. Above this temperature the field of C,H,O,Na,C,H,O,

a a 2

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44dl

extends throughout the acid portion of the diagram. Below this temperature the field of C2H30aa,2C2H,0, is bounded for a time on each side by the field of C2H30,Na,C,H,02. The exact point at which C?$&O,Na,C,H,O, ceases to exist in contact with acetic anhydride solutions is difficult to obtain experimentally. Strictly speaking, there should be a field of C,H303a on the extreme right hand of the diagram, with a non-variant point (2) where C&O,Na, (&,qOJSa,C,H402, and C2H302Na,2C,H,0, co-exist. This field should show solutions saturated with respect to C,H,O,Na, or a compound of C;IH80&a and acetic anhydride, since

C2H30,Na,2C2H,02 could not possibly be formed from C,H30,Na and acetic anhydride. It has not been possible to observe this field experimentally, but the curves point to its existence.

From 16"7O downwards acetic acid must possess a saturation field which from a point bt 16'7O must increase to the boundaries which are shown in the isotherm at Oo. ~ n . show the locus of solutions of acetic acid in water; tn shows the locus of solutions of acetic acid in acetic anhydride. These loci must merge into a point a t n, the composition of pure acetic acid at 16'7O. I n the same way, w p and wq represent the loci of the points where the acetic acid curve cuts ef, the saturation curve of

C,H30~a,2C,H40,. Theae must merge into one point a t w, where the two curves will just touch. Above the temperature at which this takes place, the saturation curves of acetic acid and C2H3O~a,2C,H,O2 will not intersect. The acid field extends between the two boundary curves m t and p u p .

DUNNINGHAH : THREE COMPONENT SYBTEM :

The following axe the numbers obtained in the experiments :

No.

1 2 3 4 5 6 7 8 9

10 11 12 13

Composition Composition of solution. of residue. -. *

N%O. (CH,*CO),O. N%O. (CH,'CO),O.

24'12 2'04 23'52 18.04 C,H30,Na,3H,0 22'55 2.62 22.69 18.24 I ,

19.82 3-83 22.23 80.36 9 ,

14'46 8-56 19.76 26.96 I 9

10'07 16'56 - - 9.81 24-66 19.52 34'26 I

9 7 2 81'00 21'06 36.95 , 9.77 33'28 21'45 36.70 $ 1

9'76 37.6 20'89 37.61 B )

9'75 40.00 21.29 38.14 9.77 41.23 20'61 41'35 C2H30,$a,3H O+ C,H,O,Na,C,H,O, 9'04 43.94 17'56 62'71 C,H,O,N~,C,I$O, 8'96 44-80 16'10 63.57 C2H,0,Na,C,H,02+ C2H,0,Na,2C,H,0,

Solid phase. % % % %

$ 9

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SODIUM OXIDE, ACETIC ANEYDRIDE, WATER.

Oo (continued).

441

N 0.

14 15 16 17 18 19 20 21 '22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

40 41 42 43 44 45 46 47 48

49 50 51 52 53 54 55

56 57 58 59 60

Composition Composition of solntion. of residue. -- .- Na,O. (CH,'CO),O. NhO. (CH,$.O),O. Solid phase.

0 , % 8'72 7.83 7 .oo 6.31 6.26 6'19 5.66 4.95 4 s o 2 1.05 0.95 0'74 0.57 0.42

2.01 2.01 2.49 2 '33 3.48

1'14 1 #41 1.84 2.06 2.19

-

-

10.14 10'08

9.03 8-88 8.23 6.72 4.56 3'56 1.25

5-01 4'89 4.36 3-19 2.10 1.88 1 *33

29.34 25'94 22.24 15.49 11 *45

ib 45.10 50 '03 55'92 59 '80 50'64 62'44 64.79 71.13 79'29 92'29 93'67 94.66 96'16 97.51 75.31 76'42 76.06 76.34 7730 77.67 90'34 90'31 90 07 88'97 87.64 87'90

28'41 40'24 43'89 4638 49.73 58'83 75.98 80'47 92'88

76'58 77'33 80'12 84.31 89.75 89.88 92'77

0'15 4.19 4'88

12.01 23'54

%, 12'64 13 '02 12.19

9.70 1035 10'02 6 '93 3'53 6'14 4'04 3'21 1'51

- -

- 1.23 0'95

1'87

0'45 0.47

1-60 2 '25

- - -

-

20'82 18'82 18.26 18.86 12.63 12.49 12.34

8.79 11'56

11.60 8'97

11'74 10.97

9-67 11-68 12.19

30'86 24'12 22'96 19'18 -

h 64.97 66.15 68'25

67-75 71'02 74.07 78.25 88.70 87.72 90'33 91'22 95.58

81.28 81.58

81.66

87.93 87-58

87'14 86.33

- -

-

- - - -

50. 35'89 C,H,02Na,3H,0 54'93 C,H,0,Na,3H20 + C,H,O,Ns,C,H,O, 64'00 C,H,O,Na,C,H,O, 66.11 64'28 C,H,O,~~,SC,H,O, 68.63 75.79 $ 9

78'89 I ,

80.61 $ 3

200. 75'11 C2H,0,Na,2C,H,0, 76.72 11

77.17 9 ,

78.92 ,* 81.25 ,* 79'68 , I

79.15 , I

15O. 13.69 C,,H,O,Na 24'35 C2H,O2Na,3H,O 27'47 , 24'81

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442 DUNNINQHAM : THREE COMPONENT SYSTEM :

No.

61 62 63 64 65 66 67 68 69 70 71 72 73 74 76

76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

93 94 95 96 97 98 99

100 101 102 103 104 105 106 107 1U8 109

15O (continued). Composition Composition of solution. of residue. &&

N%O. (CH,.CO),O. Na 0. (CH,*CO),O. Solid phase. % % 2 %

ii% 10-33 10.24 9.16 8'56 7'06 6.17 5.95 5'52 4'84 3 '44 2-87 2'16 1'02 0.79

35.31 26 '26 25.98 18.09 13'53 13.24 13'14 7 '64 7'67 7.33 0 '94 6.61 5 '52 3.78 2 '94 2.70 1.27

39'82 32'69 28'86 25.58 23.12 22.46 21.12 16'04 16.00 14.12 12'61 11.81 10.84 10.15 10'32 9.84 9'04

34.56 39'08 39.73 49.32 54'34 61.63 68.81 70.55 73'02 77.60 84.16 86.61 90.56 95'87 98.09

0.77 8-92 9.06

15'62 21.88 33.05 32'90 65'07 66.42 69'68 71'39 72.85 77.76 83.92 86.73 88'61 94.78

0.77 2 *04 6.53

14.29 18.70 18'86 19'44 26'39 33.87 36'28 41'12 44'85 51 '00 55'68 56.37 61.49 65.11

18.60 18'98 18 *27 16.85 14.72

9'11 13'13 10'64 11'22

9.68 10.75 10'16 10.75

-

-

30'00 28-61, 23.68 21'79 19'99 19.66 18'48

11-74

9.50

11.31 11'91 11.60 1094 10.72

- - -

S9.51 35'28 30.60 27 '62 22.72 22.53 22.11

21.18 18 '21 19.35 16.33 16.70 17'48 16.39 17'52 16.81

-

66*-59 64'16 62.16 63.61 86-82

71.42 74'48 74.79 77'26 79-91 79-80

-

11

C,HsO,~H,C,H,O, + C,H,OJVNa, 2C,H40 C,H,O,Ka, 2C,H40,

82.28 11

81.90 11 - , I

30°. 11'98 C2H,0aNa 18.28 .. 27.54 C,H;O2Na,3~O 31-80 11 32.72 62'78 C,HsOaNa,3H O+ C,HsO,Na,CzH,O, 5693 C;;H,O,Na, Ca€!,O,

69 '87 - C2H,0,Na,2b2H40a 72.78 11

C,H,O,Na, C H40a + C,HsOaNa 2C,H40

77.02 78.42

11

79.34 1 1

81'80 I ,

80'31 , I

450. 24'84 27.31 14'89 21'62 31'80 26.75 30.99

46'58 C ,H,O,~R,~H 0 +C,H,O,Na,C,H,O, 55'46 C,H,0,Na,C,$40, 63-66 57'24 8 ,

62.27 ,, 68-49 I ,

64-03 t ,

68 '27 I ,

69 27 110 8-86 65'74 16'33 69-54 , Y

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SODIUM OXIDE, ACETIC ANHYDRIDE, WATER. 443

No.

111 112 113 1 1 4 115 116 117 118 119 120

121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141

142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159

4 5 O (continued). Composition Composition of solution. of residue. - --

NkO. (OH,*CO),O. NkO. (CH,CO),O. Solid p h w . % % % % 8.63 68.21 15'89 70.21 C,H,O Na,C,H,O, 8.54 70.06 18'20 71.79 9,

8.20 75.06 16.06 73.27 5'54 82'16 9'52 79'34 C,H,O,Ma 2C,H402 4'64 83'64 8.59 80.87 # )

4'25 85.38 6.37 83'54 ,, 4'20 86.39 9.82 80% 9 ,

2'36 9423 10.37 83'40 1.19 97'19 9.92 85.81 C,H,O,N~,C,H,O, 0.98 98.37 11.95 84'89 2 ,

60°. 46'22 36'25 35'55 34.60 31.38 29.31 26-80 28-26 23'90 21.99 17.75 12.57 10.73 10.27 9.86

10.47 8-31 6.07 5'74 4 '25 3 '08

0 '0 1'83 2.07 2.83 4-58 7 '96

14.31 15-58 25.73 36.17 37.41 49.62 60.84 64'23 66.97 74.62 77.83 84.44 85.71 90.22 94'46

44-92 37 '63 36'18 36,113 33.32 32 '99 34.21, 29.60 26.85

20 '20 19'04 19.18 19'19 18-55 18.42 13.70

10.30 16'52 20.87

-

-

16'01 CaH,O,Na 21 -93 9 '24 1,

10.44 I 1 20-89 1s

33.51 3 )

45-52 # ¶

29'43 I #

33.54 I 1 .. - 57'64 65-14 69.26 70.36 70.92 71.93 76'80

c,H;O~N~,C,H~O, I1

1,

I ,

,, C,H,O,N~,2C,H4O2

81'54

73.27 8 ,

77-49 c,H,o,N~,c,H,o,

750. 44.45 0.76 43.78 15'54 C,H,O,Na 39.40 2.12 39.09 27'64 7 ,

35.37 3.24 36'45 29'12 I 9

32.47 5.03 34.67 25'10 9 ,

27.38 15.45 29'30 23'90 I ,

24.48 26.47 28.87 36'96 I ,

22.30 36.69 - - ~~ ..

17.85 12.78 12'13 11-05 10.54 8.84 9.02 8'61 7 *63 4.09 3.63

43.06 56-55 58.69 65.71 68.56 77'37 78.28 78.75 81'49 89.01 90.72

19.91 57.61 18.15 65.66

15.67 68'58 17.63 70.88 15.48 74'65

16.89 74'52 15'17 76'32 13.75 79-99 11-66 82'32

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_. . 160 0'44 98.35 - -

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444 TAYLOR AND B O S M C K : 1iESEARCEES ON

In conclusion, the author wishe to thank Professor Sir William Ramsay for various suggestions, and for his kindnws in revising this paper for publication.

S I R JOHN DEANE'S GRAMMAR SCHOOL, NORTHWICE, CHXBHIBE.

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