bon dioxide gas until the solution gives no color with phenolphthalein.' concentration of the aqueous solution X L t i mm. and not over 65" leaves a dry residue which i s extracted twice with 300-cc. portions of boiling ethai d , the insoluble portions reniainiiig on the filter. Hemoval of the alcohol (1.5 mm. and 50") and addition of 300 cc. of dry acetone (in which monoacetone-d-galactose and the unreacted diacetone-d-gdldctose are soluble) yields the crystalline potassium salt of diacetone-d-galacturonic acid. Addition of dry acetone to the concentrated mother liquors gives a second crop of the potassium salt, which is recrystallized by dissolving in a small volunie of ethanol and then adding acetone. The yield of the potassium diacctone-d-galacturonate is 60-80g. (49-6.5%,) : X I . p . 3C(J-205" ( d ~ . ) ; CY^% -61.1 ( 6 , 2.046; H20). Conversion of Diacetone-&galacturonic Acid Potassium Salt to Diacetone-d-galacturonic Acid.2-A solution of 60 g. (0.19 mole) of the carbonute-jree potassium salt (CleHli07KG.5H20) in sulfuric acid (376 cc. of 0.5 M ) is extracted four times with 250-cc. portions of ether. The combined ethereal extractions, dried over anhydrous sodium sulfatc, are concentrated to dryness a t 1.5 inm. and 5iJ". The residue is dissolved in 50 cc. of warm beruerie. Crystallization is induced by adding 200 cc. of petroleum cther. The yield of diacetone-d-galacturonir acid is 40 -43 g. (78-88%); n:. p. 1 3 " ; [(xj% --84.0". -
(7) I t is convenient to invert a glass funnel in a jar whose diameter is slightly greater than that of t h e fimnel. T h e carbon dioxide gas i5 ~ l i r i iintrudurrd into the soluticiii throiigh t h e stem of the funnel.
[CONTRIBUTION FROM
THE GATES AND
Hydrolysis of Dhcetoned-galacturonic Acid to dGalacturonic Acid.d--A solution of 40 g. (0.15 mole) of diacetone-d-galactiironicacid (m. p. 157") in water (120 cc.) is heated on a water-bath at 95 to 100" for two hours. After decolorizing with 5 g. of activated carbon the clarified solution should be concentrated immediately as rapidly as possible to a mobile sirup (SO', 6 mm.). The sirup is transferred to an evaporating dish and upon vigorous scratching it will set to a solid crystalline cake.s The product is collected on a Biichner funnel, washed with cthanol, dry ether, and dried over phosphorus pentoxide a t 25' and 12 mm. pressure. The yield of d-galacturonic acid is 20-25 g. (05-81 %). The product, being a mixture of the CY- and 0-forms, will show a n initial rotation of +GO" --+ +SO" depending on the time involved in concentrating the final solution. Pure a-&galacturonic acid sinters a t 110111' and decomposes a t 159-160". The [CC]~OD is -/-98" initial, final value +50.9' ( c , 2.1; HzO).
Summary An improved method for the synthesis of d ( +)-galacturonic acid has been described. The yield is 50 g. of d(+)-galacturonic acid from lo0 g. a-&galactose. ( 8 ) If the crystallization is not spontmeou, it can be induced h y the addition of absolute a l w h o l
~ I A D I S WISCONSIN ON,
CRELLIN LABORATORIES OF CHEMISTRY, CA1,IFORNIA NO. 6.241
RECEIVED J U N E 4, 19.78
INSTITUTE OF
TECIWO~.OGV,
The Molecular Structure of Arsenious Oxide, As& Phosphorus Trioxide, P,O,, Phosphorus Pentoxide, P401,,and Hexamethylenetetramine, (CH,),N,, by Electron Diffraction BY (;. c'. HAMPSON m r > A. J. S r o s I C K
I I La recent paper,' which mas published while The visual method of measurement was used, this work was in progress, there were reported the the results being compared in the usual way with results of an electroil diffraction investigation of t h e approximate scattering formula the structures of phosphorus trioxide, phosphorus I = v,, z,z, -sin - xi) .$7,, pentoxide arid arsenious oxide. The values which we have obtained for P406and As40s are in good it1 which r,j is the distance between the ith and agreement with those of &laxwell, Hendricks and j t h atoms, ZiZj their atomic numbers and s = Ikrning. On the other hand, the latter authors ( 3 x sin 8/2)/X, where 8 is the scattering angle and were unable to deduce a structure for P4010 and A the wave length of the electrons. Radial discame to the conclusion that the molecule probably tribution curves2 were also calculated and interhas lower symmetry than that of the point group atomic distances deduced from them. When a The reason for their failure probably lies tnolecule contains several approximately equal in the fact that the molecule has an abnormally distances, the radial distribution method fails to short P-0 distance and we were led to our final resolve the closely spaced maxima and very little structure, which gives an excellent fit with the information can be obtained from the curve. A photographs, o~ilyafter very many models had modification of the method, suggested by Dr. V. Schomaker of these Laboratories, in which the been shown to be wrong. eqtjmated intensities are multiplied by a factor i i ) kla.;wrll H t n r i r i c h ~ .rnri Denting J C h . i i i P L v \ 3, b X 19{71
'21
1',1171t11?
i n t i Urockway, I'IfI9 JouRv41.. 57. 2884 (19361
Aug., 1938 MOLECULAR STRUCTURE OF %ME
ARSENIC, PHOSPHORUS AND
NITROGEN COMPOUNDS 181s
TAEZLE I Max.
Min.
I
L
2
25
2
25
1.602 2.365 3.273 4.239 5.434 6.240 7.055 8.121 9.213 10.278 11.261 12.353 13.292 14.218 15.347 16.309 17.298 18.212 19.246 20.224
1
10
22.087
1 1
20
3
30
20
6
12
2 2 3 3 4 4
10
50
4
25
4
35
5 5 6
n 7 7
4
45
1
12
R R 9
9 10
in
58
I(VII1
S(VIID
rv,,/n
1.41 2.33 3.19 4.25 5.39 6.24 6.95 7.95 9.20 10.42 11.00 11.84 13.12 14.33 15.37 16.15 17.05 18.13 19.17 20.08
1.45 2.34 3.20 4.26 5.37 6.23 6.94 7.69 9.18 10.35 10.90 11.89 13.11 14.36 15.41 16.18 17.09 18.17 19.22 20.03
(0.881))
21.84
21.89
rvmln (0.905) ,989 ,978 1.005
.9a ,975 1.002 0.692
0.988
.ow
,998
1 0.9%
.€Is4
.979 ,999 1.(114 0.977
.984
,990 1.007 0.968
.w
.9.w ,987 1 .U07 1.W2
,980 1.010 1.004
0.992 ,988 .998 ,999
n.991
.9%
.m ,991; ,993
,990
11
11
.Bw)
Mean
with a chosen such that the exponential factor is equal t o one-tenth for the last measured ring, gave a satisfactory resolution of most of the distances, and was invaluable in fixing the model for P~OIO. Asroo,P40e,P,O,O,and (CHZ)~NNI were measured in Oxford using the apparatus described by de Lasz10;~for his assistance in operating the electron diffraction camera we are greatly indebted to Dr. A. H. Gregg. The measurements on Asroo, P40s,and P401awere then repeated in Pasadena nsing the apparatus described by Brockway,‘ and the two sets of results were found t o agree to within 1%. With the latter apparatus two or three extra outer rings were obtained, but the longer jet-to-camera distance employed in the de Laszlo apparatus enabled some inner fine structure to be resolved which was of great help in the PIOloinvestigation.
s*e-”’,
,9909
Mean
,991 .9W9
share of this free phosphorus was removed by irradiating the impure oxide for two days with a mercury vapor lamp. This treatment largely converts the yellow form into the much less volatile red form permitting separation by a snbsequent distillation in uacuo. The P4010used was commercial c. P.phosphorus pentoxide which was sublimed in a stream of oxygen to remove lower oxides. This treatment is necessary since the lower oxides are all more volatile. The hexamethylenetetramine was a commercial sample purified by vacuum sublimation.
Experimental The As.00used was the c. P. arsenious oxide of commerce which was not further treated. The Pros was prepared by the method of Wolf and Schmager? a modification of the older method of Thorpe and Tutton.‘ The trioxide so prepared contains 1 to 2% of free yellow phosphorus even after repeated vacuum distillation. The greater (3) Dc k l o . Prm. Roy. Sor. (London). AMs, (172 (1934). (4) Bmkway.Rn. McdwnPhyr..8),281 (1936). (51 Wolf sod Srhnugrr. &r.. El, 771 (1929J. (6) T b a p and Tutton. J . C h m . So(..67.54s (180).
Fig. L-Photomph of model of A%O.. P,O,. or (CHrhN,. The black balls represent As. P, or N: the silver balls represent 0 or CHI.
Arsenious Oxide.----The models tried for Xs,06 consist of four As atoms a t the positions (v,v,\7j, IV,V,v), (V,v,V) and (v,v,V) and six (1 atoms at the positions (+u.O,Oj, (O,*u,O) and (O,O,*u) (Fig. 1). The photographs of As400 show thirteen masima, eleven of which were measurable. The first, second and fourth maxima are strong. Preceding the fifth maximum and following the sixth maximum there are deep minima of about equal depth. The fifth and sixth maxima are of equal intensity. The values of so for the maxima and minima and the estimated intensities of the maxima are given iri Table I together with the weighted intensity values, c, used in the modified radial distributitm method. The corresponding values of 5 For rnockls VIT arid VI11 are also given.
'J'ABLB Morlel
I I1 TI1
r VI VI1 VI11
u
1'
2.310 2.057 1.890 1.890 2.038 1.981 1.959
1.355 1.308 1.160 1.142 1.142 1.142 1.142
AY--As
I1 As-0
0-As-0
3 . 2 6 a . 2.(10A. 109'28' 3.70 2.00 3.27 1.79 3.23 1.78 97"20' 3.23 1.84 102"34' 3 . 2 3 1.82 lCO"39' 3.23 1.81 99'54'
As-O~-As
109"28'
130"14' 121"58' 125'6' 126'20'
Models VI1 and VI11 lead to the following values of the interatomic distances and valence angles Model VI1 As -As = 3.20 A , AVO = 1.8U ( ) -As--0 = 100 "39' A 4 ~ - O - A=~ 125"(i'
Model VI11 As-As = 3.20 A. A - - O = 1.79.4. 0-4s--O = 99"51' i Z s - 0 - A ~ 126%)'
a.
l h e radial distribution method applied to the As406 photographs gives a curve with maxima a t 1.82 and 3.21 corresponding to the values given
A.
As,O,
above for the distances in the molecule. The curve for this calculation is given in Fig. 2. I n Fig. 3 the theoretical intensity curves for As406are
I
I
I
I
I
I
2
I
1
1
x
V I is not satisfactory because the sixth maximum has become weaker than the fifth.
In Table I1 the parameters of all the models for which intensity curves were calculated are given. Models VI1 and VI11 are both satisfactory since both are in qualitative agreement with the photographs. Model V is not satisfactory because for it the eighth maximum becomes a shelf, and model
I
1
15
10
2u
S.
Fig 3 --Calciilated intensity curves for As409.
Aug., 1938 MOLECULAR STRUCTURE OF SOME ARSENIC,PHOSPHORUS AND NITROGEN COMPOUNDS 1817 TABLE I11 Max.
Min.
I
C
1 1
'8
1
2
5
20
1
6
2
16
2
18
16
19.90
6 6
7 7
1.62 2.47 3.39 4.56 5.91 6.30 7.02 8.37 9.68 10.71 11.19 12.42 14.05 15.62 16.84 17.58 18.44 19.63
10
5 5
1.60 2.49 3.40 4.57 5.86 6.30 7.08 8.39 9.70 10.72 11.23 12.49 14.09 15.69 16.95 17.70 18.52 19.71
2.659 3.581 4.591 5.623 6.641 7.542 8.514 9.634 10.687 11.820 12.863 14.319 15.548
4 4
S(VII1)
1 ,803 2
3 3
SWI)
12 2
2
so
8 1
8 9 9
2
SVI /so
AS-AS = 3.20 As-0 = 1.80
* 0.03 A. * 0.02A.
As-0-As = 126 0-As-0 = 100
* 3' * 1.5'
Maxwell, Hendricks and Demingl give As-As = 3.20 * 0.05 A. They were unable to fix the oxygen parameter because of the much greater scattering power of the As atoms. Fair agreement was found with the oxygen valence angle As-0-As equal to 120', 127.5' or 140'. Phosphorus Trioxide.-The models used for P406 are of the same type as for As.406. The four P atoms are a t positions (v,v,v), (~,V,V),(v,v,v), and (v,V,V), and the six 0 atoms a t (*u,O,O), (0,*u,O), and (O,O,*u). The photographs of P406 show nine maxima, eight of which are measurable. The first, second and fourth maxima are strong; the second maximum is followed by a weak, almost shelf-like maximum; the sixth and seventh maxima are strong, of nearly equal intensity, separated by a broad and deep minimum; and the minimum following the weak eighth maximum is slightly deeper than that which precedes. The values of SO for the maxima and minima and the estimated intensities of the maxima are given in Table 111. Values of the parameters of models for which theoretical intensity curves were calculated are listed in Table IV. Models VI and VI11 were found to be in satisfactory qualitative agreement with the photographs. Model VI1 is unsatisfactory because the minimum following the eighth maximum has
(0.899) ( ,929) ,947 ,993 (1.051) 0.949 ,931 ,983 1.005 1.002 0 . 947 ,966 ,981 1,005
0.990 ,9802
Mean
given. As final values of the distances the following are given :
SVIII/SO
(0.887) ( .936) ,949 ,995 (1 042) D 949 939 985 1 007 1 003 0.950 ,971 .984 1.cog
Mean
0.9866 .9769
become weaker than that which precedes. Also any model with the value of the parameter u greater than that of model VI11 would make this same minimum too deep in comparison with the preceding one. TABLE IV Model
IV I
V VI1 VI VI11 I11 I1
u
1.600 1.664 1.750 1.780 1.800 1.820 1.900 2.128
w
1.064 1.064 1.064 1.064 1.064 1.064 1.064 1.064
P-P
3.010 3.010 3.010 3 010 3.010 3.010 3.010 3.010
P-0
1.597 1.620 1.654 1.666 1.675 1.684 1.721 1.843
0-P-0
90'11' 93"10' 96"53' 98'6' 98'50' 99'41' 102'36' 109'28'
P-0-P
140'48' 136"31' 130"59' 129'6' 127"52' 126'39' 121'53' 109'28'
Models VI and VI11 lead to the following values of the interatomic distances : Model VI P-P = 2.95 b , P-0 = 1.64 A . 0-P-0 = 98"50' P-0-P = 127"52'
Model \'I11 P-P = 2.94 A. P-0 = 1.05A. 0-P-0 = 99"41' P-0-P = 126'39'
A final choice of model must lie between models VI and VIII, possibly favoring model VI. This leads to the final values of the distances : P-P = 2.95 * 0.03 A. P-0 = 1.65 * 0.02 A. 0-P-0 = 99" * 1" P-0-P = 127.5 =t 1'
The results given by Maxwell, Hendricks and Demingl are: P-P = 3.00 * 0.05 A. P - 0 = 1.67 =t0.03 A. P-0-P = 128.5 * 1.5'
G. C. HAMPSON m n A. J. STOSICK
lhth
Radial distributioti calculatioiis result in a curve (Fig. 2) with maxima corresponding to interatomic distances of 1.66 and 3.03 A. The theoretical iiitcrisitv curves for 1-)40$ are given in Fig. 4. I
F,i
Vol. 60
resolved. Following the eighth measured maximum there is another doublet of which only the outer ring is measurable. The second ring of this doublet is followed by a fairly pronounced minimum and a much stronger maximum. The last measured maximum is broad, and is preceded by a well marked minimum. The minima immediately preceding and following the weak seventh maximum are both weak, the outermost being possibly a little deeper. The measured values of s o of the maxima and minima and the estimated intensities of the maxima are listed in 'Table V. In Table VI the models for which theoretical intensity curves were calculated are listed. TABLE
MRX.Min.
1
c
so
s (XIV)
sx1v/sa
10
2
17
2.823 3.965 5.015
2.82 3.75 4.91
(0.999) ( ,946) .979
IO
(i. ;300
f i , 20 i.05 8 . 50
,984
1
13 2 Absent 3 5 3 .I 8 4 6 2 3 rj 3 6 7 1 2
7.215 8,845 9.86 11.102 12.097 12.922 13.730 14.491
3.5 16
31 12
15.351
.7
x
v
I
2 27 16.043 Not measurable 1 14 18 645 9 19.662 2 27 20.470 10 21.525 1 12 22.943
,
(977
l.0lD
11.00 11.72 12.76 13.72 14.25 14.84 15.86
0.991
18.46 19.24 2O.S 21.38 23.00 Mean
990 .979 ,988 ,993 I . 003 0.9873
.969 ,988 .399
,983 .967 . 989
8
9 10 li
htodel I >
I3
10
!3J
4.
Fig. -1. - Caiculatcd intensity
111
IV
v CUI-vcs
for Pa06.
VI VI1
Phosphorus Pentoxide.-The
photographs taken show eleven measurable maxima. The second maximum is the strongest and is followed by a shelf with no observable minimum interposed; and the third maximum is moderately strong and is followed by a broad shelf-like region. On photographs which were taken using a longer jet-to-camera distance (28.0 cm.) this shelf appears as two very weak maxima with poorly marked minima interposed. With the shorter camera distance (10.S.i em.) the doublet is not
VI11
IX X XI XII
XI11 XIV
a 1.064 0.910 .903 .923 1.030 1.018 0.992 .993 1.045 1.022 1.040 1.020 1.018
b
c
'FABLE P P
VI
P-0 2.011 3.01 1.68 1,820 1.926 2.37 1 . 5 8 1.807 1.919 2.31; 1.60 1.785 1.943 2 . 8 1 1.57 1.785 1.830 2.91 1.64 1,805 1.844 2.88 1.64 1.720 2.008 2 . 8 1 1 . 5 8 1.840 1.795 2.81 1.64 1.750 1.830 2.96 1.64 1.795 1.820 2.89 1.64 1.795 1.829 2.94 1 . 8 5 1 . 8 0 0 1.836 2.88 1.64 1.792 1.827 2.88 1.63 1.820
*
P 0' OPO
1.64 1.76 1.76 1.77 1.29 1.43 1.76 1.39 1.36 1.40 1.40 1.41 1.40
POP 99'41' 126'39' 10QoZE' 109O28' 111O12' 106"4' 107'24' 112'50' 10O038' 125'24' 102'18' 122'40' lOO"36' 125O15 104" 0' 117'46' 98' 0' 129'14' 101O30' 123'42' POO018' 125'39' 101'49' 123'12' 101'39' 123'28'
All of the models are for the four P atoms a t positions (a,a,a), (Z,Z,a), (a,a,;t), and (a,S,Z), six 0 atoms a t positions (fb,O,O), (O,*b,O), and (0,0,+b), and the remaining four 0 atoms a t the positions (c,c,c), (C,C,c), (C,c,F), and (c,C,C). Models XI, XI11 aiid XIV are all satisfactory iii
Aug., 1938 MOLECULAR STRUCTURE
OP %ME
ARSENIC, PHOSPHORUS AND NITROGEN COMP~UNDS 1819
their qualitative agreement with the photographs. Model XIV is rouzhlv the mean of models XI and XIII, and it has be& used for the final calculations of the interatomic distances of the molecule. The following distances result from these calculations:
--
P-P * 2% * 0.03 A. P-O 1.62 * 0.02 A. P-O' 1.39 * 0.02 A.
The theoretical intensity curves for the models of Table VI are shown in Fig. 6.
--
101.5 * 1' POP 123.5 * 1' OPO' = 116.5 * 1'
OPO
The angle designated by OPO' is the angle formed by the P atom at (a,a,a) and the 0 atoms at (b,O,O) and (c,c,c) (Fig. 5). It may be seen from an inspedion of the models listed that the valence angles are very closely limited. Model XI1 dam from model XI only in the phosphorus d r d i n a t e s , causing a change in the P valence angle of only about one degree, but it is not in qualitative agreement with the photographs in that for it the shelf-like region following the fourth maximum has become a real maximum with a preceding minimum. The short P-O' distance is also fixed closely by the disagreement of model VII. This model daers from the satisfactory models only in that the coordinates of the outer four 0 atoms arechanged by a very small amount.
c
s.
1-
5
I
I
I
10
15
20
s. Fig. 6.--Calculatcd intensity curves for P4010.
Hexamethylenetetramine.-The photographs of this substance were taken using a long jet-tocamera distance and show six maxima. The iirst two are strong, the third broad and M u s e , the fourth very weak, the fifth fairly strong and the sixth very weak. The hexamethylenetetramine model is essentially the same as that for P,OS and As,Oc Four N atoms are in positions (v,v,v), (V,V,v), (T,v,V) Fig. S.-Photograph of model of P,Om The and (v,?,V), six C atoms in positions (*u,O,O), black balls rep-qt P; the silver balls repre(O,*u,O) and (O,O,*u) and the twelve H atoms snt 0. in positions (x,?,~), (Z,x,z), etc. The hydrogen The m d e d radial distribution method sug- parameter could not be deduced from the photogested by Dr.Schomaker gave a remarkably good graphs and an assumed value of 1.09 A. for the resolution of the various peaks, nearly all the in- C-H distance was used in computing the theoretiteratomic distances in the molecule appearing as cal intensity curves. A model in which all the separate maxima. The curve is shown in Fig. 2. angles had the regular tetrahedral value of 109.5" From the data which i t provided, the three par- and with a C-H distance of 1.48 A. (N-N or C-C ameters could be determined within narrow limits, = 2.42 A.) was found to agree well with the photothese parameters agreeing well with those chosen graphs. The curve for this model is shown in for the final model. Fig. 7. Table VI1 gives the measured values of
(i.C. WAMPSON
1rim
1
IO
AND
I r,
c
Fig. 'i.--Calculated intensity curve for (CH2)&(. S O for the maxima and minima together with the estimated intensities of the maxima; the s values for the above model are also listed, and the average value of $/so is seen to be practically unity.
c
2.93 4.00 5.50 7.15 9.41 10.75 11 .40 12 . : 3 5 13.68 16.2e5 Mean
c/
(J
CI
988 953 993 979
1 Ci3 1 020 0 995
0 989
1.012 1 029 I 003
'The radial distribution curve shown in Fig. 2 gives C -X = I A7 A.and C-C or N- N = 2.43 A. agreeing well with the above model.
Discussion of Results Of the substances reported in this paper, two, hexamethylenetetramine and arsenious oxide, have been studied in the solid form. Hexamethylenetetramine crystallizes in a body-centered cubic lattice, Dickinson and Raymond7reporting a regular tetrahedral arrangement of valences with CN = 1.44 A. Gonell and Mark8 gave C-N = 1.48A. and C-C = 2.58 .&., and this same type of structure has also been confirmed by Wyckoff and Corey,Ywho give C-N = 1.42 * 0.08 A. The sum of the covalent single-bond radii1° of carbon and nitrogen is 1.47 A. in good agreement with the value which we find here. Arsenolite, cubic AseOe, was reported by Bozorth" to be a lattice of AsrOr,molecules in a diamond-type arrangement. Both the As and the 0 (7) Dickinson and Raymond, THISJOURNAL, 45, 22 (1923) (81 Gonell and Mark, Z physik Chrm , 107, 181 ( 1 9 2 3 (9) Wyckoff and Corey Z K r t < t . , 89, 462 (1934). ( I O ) Pauling and Huggins, ibzd ,ST,205 (19.34) '11) Bosorth, T ~ r s J o i r ~ h46, ~ 11621 '11123)
A. J . STOSICK
1'01. tic)
valence angles are tetrahedral in this solid, the As-As distance 3.28 A. and the As-0 distance 2.01 8. There are two strong bonds for each 0 atom to two As atoms in the same molecule, and two weak bonds to two As atoms of a neighboring molecule. This attraction between neighboring molecules apparently draws the 0 atom out, increasing the As-0 distance and decreasing the oxygen valence angle from the values observed for the vapor molecule to those observed in the solid. To a smaller extent this applies to the As atoms too, since each forms three strong bonds to oxygens in the same molecule and three weak bonds to oxygens of adjacent molecules. A redetermination of the crystal parameters was made by Harker and Eskijian12 in these Laboratories confirming the older values but fixing them more closely (to within about 0.03 A.). Arsenic apparently has a tendency to form bonds at angles smaller than the tetrahedral angle, as As406 is not unique in this respect. In this compound where the atoms form closed rings it might be thought that the As valences are strained into taking up this angle because of the tendency of the oxygen angle to expand beyond the tetrahedral value13 but even in compounds where the groups attached to the As atom form no other bonds, the As bond angle is considerably less than 109°28'. Examples are AsCls 103°,14,16101 * AsBr3 100 * 2O,l6A s ( C H ~ )96 ~ * The remarkable constancy of this angle of around 100' already has been remarked upon.Ib Steric effect and electrostatic repulsions are so different in this series of compounds that they cannot be the deciding factors in fixing the angle According to the theory of directed valency'* the utilization of p orbitals alone leads to the formation of bonds which are mutually perpendicular. Hybridization with the s orbital gives rise to stronger bonds which, if hybridization is complete, as with carbon compounds, are at an angle of 109'28'. If, however, there are unshared electrons, as in the case we are considering, hybridization may not be complete, for there are two opposing tendencies. On the one hand, hybridization tends to stabilize the bonds but a t the same (12) Unpublished work (13) Sutton and Hampson, Trans Faraday Soc , 31,945 (1935) (14) Brockway and Wall, Ters JOURNAL, 66,2373 (1'334) (15) Pauling and Brockway, J Chem Phys , 2, 867 (1934) (16) Gregg, Hampson, Jenkins, Jones and Sutton Ti a n > Fni aiinx k ~ c 93, , 852 (1937) (17) Spnngall and Rrockway 1.~15 JCVRNAI , 6 0 , 99fl 11918) ( i l l ) Paulinn rhid 63, 1367 (1'131)
Aug., 1938 MOLECULAR STRUCTURE OF SOME ARSENIC,PHOSPHORUS AND NITROGEN COMPOUNDS 1821 time this means that the unshared electrons also tend to become hybridized between the s and p orbitals, whereas the unshared pairs of electrons are always most stable when they occupy the s orbitals. As usual the actual configuration taken up is that which gives the lowest energy. The sum of the covalent single-bond radii1° of arsenic and oxygen is 1.87 A. The decrease from the sum of the radii to the observed value of 1.80 A. may be explained as the result of double bond character caused by unshared pairs from the oxygen atoms forming double bonds with the As atom^.'^--'^ The value 126 3” which is observed for the oxygen angle is close to 125’16’, the angle between a double and a single bond on the regular tetrahedral model. Phosphorus, like arsenic, shows a tendency to form bond angles less than the tetrahedral angle. In P406 it is found to be 99’. Inlother substances where the groups attached form no other bonds the same behavior is noted. Examples are PF3 99 * 40,14 PCl3.10O * 20,14 PBr3 100 * 20,16 PI3 98 * 40,16Poc&1 0 4 O , ” P(CH3)3 100 += 4 O . l ’ The sum of the covalent radii1° for phosphorus and oxygen is 1.76 k. Again the observed value is lower presumably because of double-bond character, as with Ashoe. In P4010 the phosphorus angles are 101.5 and l l t i 5 ° . The latter angle is that between an outer oxygen atom and one within the Pro6 “kernel.” Addition of this outer oxygen atom has had very little effect on the other bond angles and this might have been anticipated from the values given for PCb and POC13. The most startling feature of the P 4 0 1 0 molecule is the unusually short distance of 1.39 A. between each P atom and the “extra” 0 atom. The value found is about 79% of the sum of the single bond radii (1.76 A.) and is approximately that expected for a triple bond between the two atoms. A similar anomaly has been observed in thiophosphoryl chloride, PSC13,20 where the P-S distance is found to be 1.94 b. instead of the normal single bond distance of 2.14 A. It is clear that double bond character in a structure such as
/oI, \o-
O=PLO-,
is not sufficient to explain such a large shortening as is observed. The addition of four extra oxygen atoms to P4O6 has very little effect on the dimensions of this P4O6 “kernel,” and since we have (19) Rrockway and Beach, THIS JOURNAL, 60, 1836 (1938). (20) Beach and Stevenson, J . Chcm. Phys , 6,75 (1938).
postulated single-double bond resonance in P406, it seems reasonable to conclude that it also occurs in P4010. The important systems are probably I1 and I11 in resonance with I.
+
O-P-O-P-
+ - /o0-P-0-
\O-
\O-
I1
111
There is another piece of evidence which favors this conclusion. In P40e the contribution of a -NO+was postudouble-bonded structure IV P-0-
\o-
lated to explain the shortening of the P-0 bond below the single bond value. In this structure the phosphorus and oxygen atoms carry opposite charges and so there is no “formal charge effect”21 influencing the bond length. On the other hand, in structures I1 and I11 of P4010the positive charge on the oxygen or phosphorus atom is not compensated by a negative charge within the P406 “kernel” and hence because of the increased &ective nuclear charge we should expect the bond length to be diminished. The P-0 distance in P406is 1.65 A. and the corresponding distance in P& is indeed shorter, being 1.62 A. The difference may be due to experimental error, although in view of the above argument it may be of some significance. As regards the other P-0 distance having the extremely low value of 1.39 k., the “formal charge effect” in structure I1 (negative charge on the oxygen, no charge on the phosphorus) would lead one to expect an increase rather than a decrease. One is forced to conclude that the predominant factor here must be the polar character of the bond. In discussing PSC4, Beach and Stevensonz0ruled out any effect of ionic character and formal charges on the length of the bond, but concluded that the shortening of the P-S distance must be due to a con-
/Cl+
siderable (about one half) contribution of S-P-CI
\Cl
without, however, giving any reasons. The short P-0 distance in P4010is in accord with the chemical properties of this molecule. Such short bonds are presumably extremely stable, and the thermal stability and resistance to reduction of P4010 are well known. We wish to express our thanks to Professor Brockway, Professor Pauling and Professor Sidgwick for their help and interest in this work, (21) Elliott, THIS JOURNAL, 69, 1380 (1937).
1x22
h K O Y
H. ANDERSON AND
a i d the Commonwealth Fund for a Fellowship to of 11s (C.C. H.)
OllC
Summary Electroil dBractio1i measurements on arsenious oxide, phosphorus trioxide and hexamethylenetetramine show that the molecules consist of four phosphorus or nitrogen atoms in positions ( w v ) ( E v ) (VvV) and (vVV) and six oxygen atoms or methylene groups in the positions (*u00) (0 * u0) and (00rf: u). In phosphorus pentoxide there are four additional oxygen atoms in the positions (www) (WiTw) (ZwW) and (wWW). The interatomic distances and angles are: for A \ ~ d 0 6 , AS-0 = 1.80 * 0.02 K . , 0 AS 0 = 100
DON
hf.YOST
Vol. ti0
* 1.50JAs-0-As = 1% * :3’, for P ~ O SP-0 , = 1.65 * 0.02 A., 0-P--0 = 99 * l o ,P-0-P = 127.5 * lo,for N4(CH2)6, C-N = 1.47 * 0.02 A., C-N-C = N--C--N = 109.5’, for P4Ol0,P-0 = 1.62 * 0.02w., P-0’ = 1.39 * 0 . 0 2 ~ ? 0-P-0 ~., = 101.5 * l o ,P-0-P = 123.5 * 1’ and 0-1’-0’ = 116.5 ==I l o . The shortening of the bond distances in As40BI P ~ O Sand Pa0,0 below the theoretical single-bond values is attributed to single-bond double-bond resonance. It is concluded that the abnormally low value of 1.39 A.for the P-0’ bond in P4O10is due to the polar character of the bond. PASADENA, CALIF.
KBCElVED
MAT31, 1938
ICONTRIBU 11ON FROM I‘IW, GATES AND CRBLLIN LABORATORIES OF CHEMISTRY, CALIFORNIA INSTITUlB OF ’rECHNOLOGY,
No. 6471
The Properties of Qsmiutn Tetroxide in kbT The Thermodynamic Constants of 0-
Notide Solutions.
BY LEROYH. ANDERSON AND DONM. YOST
Introduction Osmium tetroxide is known to be moderately soluble in water and very soluble in carbon tetrachloride. Von Wartenberg2 determined the solubility to be 6.47 g. per 100 g. of water, and about 350 g. per 100 g. of carbon tetrachloride, at 20”. The distribution ratio of osmium tetroxide between carbon tetrachloride and water was determined by Uost and White3 for dilute solutions to be 13 when the concentrations are expressed in moles per liter of bath solvents. Distribution ratios were determined independently, and a t about the same time, by Tschugajefi and Lukashuk4 with essentially the same results. These authors also made solubility determinations in water but the result, 6.23 g. per 100 g. of water a t %5’, does not seem t o be consistent with that of Von Wartenberg. The distribution ratio calculated from solubilities is much higher than that found in the experiments on dilute solutions. This fact indicated that either the concentrated solutions in (1) Presented a t the Second Annual Symposium of the Division of Physical and Inorganic Chemistry on the Less Familiar Elements,
Cleveland, Ohio, December 27, 28 and 29,1037. (2) Van Wartenberg, A n n Chpm, 440, 97 (1924); 441, 318 (1925); Bichowsky and Rossini, “Thermochemistry of Chemical Substances,” Reinhold Publishing Corp , N e w York, N Y , 1936, p 82 (3) E’ost and White, Trns JOURNAL, 60, 81 (1928) (4) Tschuhajeff and I ttkashuk 2 anoig Chem , 173, 223 (1928)
carbon tetrachloride were exhibiting some abnormal behavior, or that in the distribution experiments water possibly was associated with the tetroxide in carbon tetrachloride layer, thus forming a different solute. In order to settle this point, distribution experiments were made with solutions whose concentrations varied from very dilute t o saturation, the solubilities of osmium tetroxide in both water and carbon tetrachloride were redetermined, and the vapor pressures of carbon tetrachloride above solutions of osmium tetroxide in i t were measured for the range of concentrations up to saturation.
Prepamtion of Materids and Experimental Methods OBmium Tetroxide.-Osmium metal freed from ruthenium was heated to 300-400° in a glass tube in a stream of dried oxygen. The vapors of osmium tetroxide (b p. 130’) were condensed in the distribution vessel or capsules by means of a solid carbon dioxide-alcohol bath. All other chemicals used were of the best grade obtainable. The carbon tetrachloride was further purified by fractional distillation. Analytical Methods.-Osmium tetroxide is frequently determined i o d i ~ e t r i c a l l y ,but ~ ~ ~the colored tetravalent osmium solutions hide the end-point in all but rather dilute solutions, and atmospheric oxygen affects the results. After some experimentation the following procedure was [a) ( 1
