I
E. J. GRlFFlTH Inorganic Chemicals Division, Monsanto Chemical Co., St. Louis, Mo.
A Nomograph for the Hydrolytic Degradation of Pyro- and Tripolyphosphates
S I ~ C E 80
the first article appeared in 1852 ( 6 ) . about investigations have been reported. involving the variables in hydrol>-tic degradation of condensed phosphates. T h e relative magnitudes of these variables for dilute solutions of pure alkali metal salts of the simpler phosphate anions (pyro-. tripoly-. trimeta-, and tetrametaphosphates) are \veil understood. Hobvever, the influence or enzymes (1.S), hydrous metal oxides ( 7 . 2 ) . a n d multivalent cations ( 3 )is lraguely understood. S o work has been reported to prove lvhether or not
degradation of condensed phosphates is a photoactive process. T h e nomograph for the half life oi pyro- a n d tripolyphosphates. as a function of temperature and p H . has been constructed from the work of \.an\Vazer. Griffith: and McCullough (7). It is based upon the tetramethylammonium salts of the phosphates. tvhich \vere chosen because the (CH3)41\'- ion cannot form complex ions with the phosphate anions. and the extraneous factors ivhich may be attributed to metal ion catalysis and solvated supporting electrolvtes are .*
.,
Io,ooo,oo 0
This nomograph for the hydrolysis of pyro- and tripolyphosphates can be used for estimating the half life of other systems
$00~000
-
2,000,000
1,000.000 1-
-
500,000
200,000
Factors and Conditions
100.000 7-
50,ow
-
20,000
-
10,000 y5.000
-
2,000
-
120-250
PH PY R O I3
-
zoo
-
Io
100--212 -200
so--
l,ooo~500
IIO--P30
80--I8O
TRIPOLY
oj-
70-- I 6 O 60-- I 4 0
50--
I2 0
50
-
40--
20
-
30-
1 0 ; -
e+-
5 -
IO0
-
80
-
60
lo--
-
217-
0.5
0.2
-
0.1-
240
INDUSTRIAL AND ENGINEERING CHEMISTRY
0-
40 32
Sodium phosphate IpH less than 1 1 ) Sodium phosphate plus 10% sodium chloride (pH 4 and greater) P o t a s s i u rn phosphate (35% solids)
Multiply by
0.7
0.5 0.35
avoidrd. 'I'hus. any valur of half life \vhich is obtained from the nomograph may be converted to half lives for thc phosphate salts of the alkali metals simply by multipl>-ing the half life by thc appropriate factor. For example, the half life of sodium tripolyphosphate is about 707, of the half life for tetramethylammonium tripolyphosphate under similar conditions a n d a factor of 0.7 applied to the nomograph yields a good estimate of the half life of sodium tripolyphosphate. .4t low pH values (less than pH 4) exccss sodium ions inhibit the reaction rates and a t high pH values ( p H 11 and greater) excess sodium ions arcelerate the reaction. To construct the nomograph. a mathematical expression was needed for the relationship of half lifee?p H . and temperature. 'Phe hall life is not a simple function of pH and temperature. if great precision is required. T h e equations may be simplified? however. to yield results lvhich are approximately correct and greatly reduce the work required in constructing the nomograph. 'This \vas done for the nomograph under consideration. T h e error introduced by simplifying the mathematics \vas about +5% but this is not particularly serious because the nomograph cannot be read Lvith much greater certainty. .At worst. the nomograph yields a good estimate of the half life of the phosphates when applied to pure aqueous solutions of the phosphates a n d extraneous factors-e.g., enzl;mes. heavy metal ions. othersare avoided. T h e approximate effects of eni4ronmental impurities upon the rate of the degradation of phosphates Lvere outlined by Karl-Kroupa, Callis, and Seifter 1.5). literature Cited (1) Barnann, E., Heumiiler. E., S a i u r zcissenschaflen 28. 535 11940). ( 2 ) Barnan:, E., heisenheimer, M., Ber. 71B, 2086, 2233 (1938). (3) Green, J., IND. ENC. CmM. 42, 1542 (1950). (4) Ingelman, B., Malmgren, H . , ilcta Chem. Scand. 1 , 422 (1947); 2, 365 (1948); 3, 157, 1331 (17471. (5) Karl-Kroupa, E., Callis, C. F., Seifter, E,. IND.E m . CHEM.49, 2061 (19573. ( 6 ) Reynoso, A , , Ann. Chem., Justus Lwbiqs 83, 98 (1852); Compt. rend. 34,795 (1852). (7) VanWazer, J. R., Griffith, E. J., McCullough. J. F., J . Am. Chem. Soc. 7 7 , 287 (1955). RECEIVED for rwiew July 18, 1958 .ACCEPTED November 11. 1958
