HYDROGENATION OF ALIPHATIC NITRILES OVER TRANSITION METAL BORIDES C L l V E
B A R N E T T '
Petrochemical and Polymer Laboratory, I.C.I., I&., The Heath, Runcorn, Cheshire, England Iron, cobalt, nickel, platinum, ruthenium, rhodium, and copper boride catalysts for the hydrogenation of propionitrile, butyronitrile, and acrylonitrile were investigated. The product spectrum, catalyst activity, and effects of medium and other metal additives on these catalysts were studied. In the absence of alkaline additives, a mixture of primary, secondary, and tertiary amines is formed. Nickel and cobalt boride are the most effective for primary amine formation, rhodium boride for secondary amine formation, and platinum boride for tertiary amine formation. The borides are more selective and more active than the corresponding metals. In the hydrogenation of acrylonitrile suppression of secondary and tertiary amine formation by the addition of ammonia is complicated by the addition of ammonia to C=C. An acrylonitrile-anthracene adduct was hydrogenated to give allylamine as the major product.
THEheterogeneous,
catalytic hydrogenation of nitriles has long been used for the preparation of amines. Various catalysts have been used and the products are a mixture of primary, secondary, and tertiary amines, the nature of which lis dependent on the catalyst as well as on temperature, pressure, and reaction media. Secondary and tertiary amine formation can be suppressed by addition of a large excess of ammonia (Grunfeld, 1948; Schoegler and Adkins 1939; Young and Christenson, 1942) or other alkalies, or by formation of a salt with an acid (Hartung, 1928) or better still by acylation (Carothers and Jones, 1925). Deactivation of the catalyst frequently occurs, but ammonia is the least deactivating. Cobalt boride is highly selective in the hydrogenation of adiponitrile (Polkovnikov, 1959) t o hexamethylenediamine. Hydrogenations using nickel and cobalt borides indicate that these catalysts are highly active and resistant to fatigue (Hofer, 1964 Paul et al., 1952; Thonnert et a l , 1964). The borides also show high selectivity in the hydrogenation of olefins (Brown and Brown, 1950) and carbinols (Alder and Marton, 1961). Controlled hydrogenation of unsaturated nitriles to unsaturated amines is difficult. Under normal circumstances the C = C group is more susceptible to hydrogenation than the C = N group, and the reduction of acrylonitrile using copper (Reppe and Hoffman, 1932) and nickel (Winans, 1942) yields propionitrile initially. I t has been reported (Armour and Co., 1955), however, that unsaturated amines can be obtained from tallow nitriles by reduction with copper chromite catalyst, but these are secondary rather than primary amines and a different mechanism has been postulated. I t has been reported (German Patent Application, 1935) that unsaturated nitriles form 9:lO adducts with anthracene. Such adducts of olefins and nitriles are not uncommon (Bruson, 1942; Iflowry, 1947).
Present address, LVorks Research and Development DepartDalton Works, Imperial Chemical Industries, Ltd., Huddersfield, Yorkshire, C.K. I
ment,
Formation of an anthracene adduct followed by hydrogenation and decomposition of the product by destructive distillation would seem to afford a fairly selective hydrogenation of unsaturated nitriles to unsaturated primary amines. Selective hydrogenation using this method of double bond protection is known for dienes (Slaugh and Magoon, 1962; Smith and Holm, 1956). The present work was undertaken to compare metal boride catalysts with each other and with the corresponding metal catalysts, for the hydrogenation of saturated and unsaturated nitriles, and observe the effects of other metals as additives. The comparison was made on the basis of activity, selectivity, and ease of deactivation. Another objective was to hydrogenate acrylonitrile catalytically to n-allylamine. Experimental
Apparatus. A Cook Hydrogenator was used. This consists of a thick-walled glass reaction bottle (600-ml.), placed inside a rocking chamber containing a heating element. The lid of this chamber clamps down and seals the bottle with a rubber plate. Two tubes through the lid and rubber plate allow hydrogen to be fed into the reaction vessel from a reservoir. The temperature is measured by a thermocouple. Materials. Metal and metal boride catalysts were prepared from their nitrates or chlorides (Analar grade) and were supported on kieselguhr (British Drug Houses, laboratory grade), microspheroidal silica (Peter Spence) , or activated charcoal (1000 to 2000 microns). Solvents and reactants were purified by double distillation and shown by GLC to be single components. The method of catalyst preparation is illustrated by the following examples. VOL. 8 NO. 2 JUNE 1 9 6 9
145
...
...
67 26 43 19
30 10 7
...
...
50 54
... ... ...
3 2 3 1
97 98 49 45
24
7
75
18
...
I.P.A.'
24
11
80
9
...
I.P.A.'
24
27
61
12
I.P.A.'
24
32
60
8
... ...
I.P.A.'
24
15
71
14
...
I.P.A.'
24
17
67
16
...
COBALT BORIDE (5%) ON CHARCOAL.Charcoal (20 grams) in distilled water (8 ml.) was soaked for 15 minutes. Cobalt nitrate (4.2 grams) in water (20 ml.) was added and the mixture heated gently to dryness. The charcoal was cooled in ice water and sodium borohydride (25 ml. of 20% solution) was added, slowly to avoid rapid effervescence. The mixture was allowed to stand for 16 hours, was filtered, and the catalyst was washed with copious amounts of water, then dried and stored under hydrogen. Although not pyrophoric, the catalyst became deactivated on standing in air. RANEYCOBALT.To a well-stirred solution of sodium hydroxide (12.8 grams) in water (50 ml.) was slowly added Raney cobalt alloy (10 grams), while the temperature was maintained a t 50" to 55°C. The mixture was then digested for 1 hour a t 50" C. with stirring, and the catalyst was washed with water (about 20 liters) by continuous decantation, then with ethanol, and finally by the solvent to be used in the hydrogenation, and used immediately. COBALT(5%) ON KIESELGUHR.Cobalt nitrate (10.8 grams) was deposited on kieselguhr (80 grams) as above. The catalyst was reduced in a Cook Hydrogenator at 3 atm. and 70" C., immediately prior to use. COBALTBORIDE (5%) ON CHARCOAL WITH METAL ADDITIVES. Cobalt nitrate (4.2 grams) was deposited on charcoal (20 grams) and treated with 50 cc. of ruthenium chloride (0.270)~ chloroplatinic acid (0.2%), nickel chloride (0.5%), rhodium chloride (0.5%), titanium trichloride (0.5%)) cupric nitrate (0.5%), or ferric nitrate (0.5%). The mixture was evaporated to dryness and reduced by continuous decantation, dried, and stored under hydrogen. Hydrogenation Procedure. Each experiment was carried out using 1 gram of catalyst, 0.25 mole of nitrile, and 300 ml. of solvent, in a Cook Hydrogenator. The experiment was continued until the uptake of hydrogen finished or for a predetermined time. The products were analyzed by GLC and by isolation of the components by fractional distillation. Results by both methods were in excellent agreement (Tables I to IV). Anthracene-Acrylonitrile Adduct. Anthracene (12.5 grams, 0.07 mole) and acrylonitrile (3.7 grams, 0.07 mole) in 1to 1 isopropyl alcohol-n-hexane (200 ml.) were refluxed for 1 hour under an atmosphere of nitrogen. The catalyst (0.5 gram) was added. Nitrogen atmosphere was replaced by hydrogen a t 1, 2, or 3 atm. and the temperature was raised to 100°C. When the uptake of hydrogen had ceased or after a predetermined time interval, the hydrogen was again replaced by nitrogen. The adduct was decomposed by heating and distilling off the products as they were formed until the bath temperature reached 250" C. and was maintained there for 1 hour to make certain that the adduct had completely decomposed. The product was analyzed by GLC and by isolation of the components by fractional distillation. The results are summarized in Table V. Mass balances are less than 100%. I n all cases, after the amines, nitriles, and anthracene had been isolated, there remained a high boiling tarlike material which was not identified.
I.P.A.'
24
19
42
23
16
Results and Discussion
Table 1. Propionitrile Hydrogenation"
Time, Catalyst Cobalt boride
Rhodium boride
Nickel boride
Cobalt
Rhodium
Nickel
Iron boride
Copper boride
Ruthenium boride
Solvent
Hr.
PN
Water' Waterc I.P.A.b I.P.A.' I.P.A.d Acetic' acid Ac~O'
26 26 26 26 26
...
Cobalt boride + Rh Cobalt boride + Ni Cobalt boride + Ti Cobalt boride +cu Cobalt boride + Fe Cobalt boride + Ru Cobalt boride
+ Pt
5 10
... 31
... ... ...
69 90 78 83 99
...
57 100
...
...
Waterb Water' I.P.A.' I.P.A.' Liquid NH, Aceticb acid Ac2Ob
32 72
Water' Water' I.P.A.b I.P.A.'
26 26 26 26
Waterb I.P.A.b I.P.A.'
26 7 7
... 46 73
64 40 27
Waterb Water' 1.P.A.' I.P.A.'
26 26 26 26
... ... ...
... 9 ...
12
Waterb Water' I.P.A.' I.P.A.'
26 26 26 26
... ...
Water' Water: I.P.A. I.P.A.'
28 10 17 7
8
16 16 16 16
...
...
31
29
61 86 66 35
2
...
98
...
35
... ... . ., . ... 27
14
...
36
100
...
63 89 65 73
37 11 35
... 36 14
...
...
...
...
...
... 4
... 39
... 34 5
... 29
... ... ... ...
... ...
...
...
32
58 75 61 50
42 16 39 6
36 23 43 5
... ...
31
64 77 57 64
26 26 26 26
67 75 67 75
19 23 20 17
9 2 10 2
Waterb WaterC I.P.A.' I.P.A.'
26 26 26 26
71 68 73 81
11 22 10 17
4 2 9
Waterb Water'
...
...
...
I.P.A.'
24 24 24 24
64 50 69
Waterb Water' I.P.A.b I.P.A.'
24 24 24 24
... ...
I.P.A.'
I.P.A.' Platinum boride
32 72
...
Mole % Yield PrNH2 Pr2NH Pr3N
...
... 11
... ... 3
... 2
... 4
... 4
' 7P C. at 2-atm. pressure. ' N o ammonia added. e Amm0nia:nitrile 5 : l . Ammonia:nitrile l 5 : l . PNpropionitrile, PrNH, n-propylamine, Pr2NH dipropylamine, Pr3N triprupylamine, I.P.A. isopropyl alcohol.
146
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
Primary, secondary, or tertiary amines can be obtained in good yield from saturated nitriles by selection of the appropriate catalyst and conditions. I n general, cobalt boride appears to be the most selective catalyst for primary amine formation, with nickel boride
~
~~
Table 111. Hydrogenation of Acrylonitrile over Copper Chromite Catalyst"
Table II. Butyronitrile Hydrogenation"
Solvent
Time, Hr.
Water' Water' 1.P.A.O I.P.A.'
16 16 14 14
Water" Water' I.P.A.@ I.P.A.'
16 16 24 24
I.P.A.t' I.P.A.'
Copper boride Iron boride
Catalyst
Mole %b Yield BN
BuNH2 Bu2NH Bu3N 67 86 72 79
28 14 17 5
...
3 2
21
27
59 98 62.5 52
38
...
... ... ...
24 24
14 17
68 81
18 2
...
I.P.A." I.P.A.'
14 14
81 86
8 10
8
3
I.P.A.b
14
72
14
8
2
I.P.A.'
14
80
10
3
...
Ruthenium boride
I.P.A.' I.P.A.'
14 14
18 21
32 51
44 28
...
Platinum boride
I.P.A.' I.P.A.'
14 14
62 64
... ...
8 6
30 30
Cobalt boride
Rhodium boride
Nickel boride
5
... 11 10
...
... ... ... 37.5
...
...
. . . . . .
6
% Molar Yield
Time, Hr.
Allylamine
Diallylamine
Triallylamine
...
...
13 15 17 19 18 16 7 15 13
12 21 33 41 54 67 67 35 16
... ... ... ... ...
100 75 63 40 36 26 13 20 24 33
1 3 6 12 24 48 72 48' 24' 24K
'
... ... ... ... . . . . . . ... ... ... ... . . . . . . . . . . . . ... ...
... ... 11
...
14 24
...
10 13
"100" C. at 3-atm. pressure in 15,; aqueous NaOH solution. Ammonia added only where indicated. 'Acrylonitrile. CNCH2CH2NH2. (CNCH,CH,),NH. e 100" C. at 3-atm. pressure in water. 'Ammonia:nitrile 1 :1. 'Ammonia:nitrile 5 : l .
Table IV. Hydrogenation of Acrylonitrile-AnthraceneAdduct
7P C. at atm. pressure. b N o ammonia added. 'Ammonia:nitrile 5 : l . B N butyrunitrile, BuNHz n-butylamine, Bu2NH dibutylamine, BulN tributylamine. a
Molar % ' Yield PresTemp., sure, Time, n-Allyl- n-PropylAtm. Hr. A N PN amine amine
Catalyst
O C .
Rhodium boride on carbon
only slightly less effective. This is in agreement with other work in which Raney catalysts have been used (Petrov et al., 1960; Reeve and Edreckson, 1950). Rhodium boride is a fairly selective catalyst for secondary amine formation, and, in the absence of ammonia, no primary amines have been detected, although tertiary amines are formed. Platinum (Rylander and Kaplan, 1964; Rylander and Steele, 1965) has been claimed to be a selective catalyst for tertiary amine formation, and the results in Tables I and I1 confirm this. Ruthenium, copper, and iron borides have no utility. The solvent often has a profound effect on the product distribution and catalyst deactivation. For nickel, cobalt, and rhodium borides, 2-propanol (I.P.A.) is preferred to water, giving rise to g,reater selectivity, whereas platinum boride is severely deactivated in 2-propanol. When ruthenium boride is used, primary amines are detected only with 2-propanol as solvent, while tertiary amines are more easily formed in water. I t is perhaps surprising that hydrolysis products were not detected, and it can only be assumed that the conditions were sufficiently mild to prevent hydrolysis from occurring in water. I n acetic acid, selectivity towards primary amines is improved, and in acetic anhydride wit'h all catalysts primary amines are the sole products, but the nickel, rhodium, and cobalt borides are deactivated in both. I n addition to the metal boride catalysts, cobalt, nickel, platinum, and rhodium were used in the form of metal on carbon; but it was clear that the metal boride was the most effective form. The borides were more selective, more active, and less inhibited by solvent and ammonia. On the other hand, the over-all pattern is not altered, and mixtures are obtained for metal and metal boride catalysts. With the exception of platinum boride, secondary and tertiary amine formation can be suppressed by the addition
70
81 . . . 8 0 ... 72 2 7 5 52 . . . . . . 13
3 7 10 69 27 44
...
... 6 47 . . . . . . 17
76 . . .
10 68 31 41
..
70 . . . 5 40 3 . . . 18
12 61 35 40
4 8 5 19
4 52 22
...
100 70 140
3 3 3
10 2 4 72 48 48 48
Cobalt boride on carbon
70 100 70 140
1 3 3 3
48 48 48 48
Nickel boride on carbon
70 100 70 140
1 3 3 3
48 48 48 48
Ruthenium boride 70 on carbon 100 140
1 3 3
48 48 48
81 7 24
...
Iron boride on carbon
70 100 120
3 3 3
48 72 100
47 23
...
25 40 57
...
4 ... 10
Copper boride on carbon
70 100 140
3 3 3
48 72 100
59 . . . 46 9 4 15
11 23 17
...
1
...
9 14
... ... 2
...
... 5 3 22
3 12 6 12 14 35
Table V. Addition of Ammonia to Acrylonitrile"
Boride Catalyst
Pt Ru Ni co Rh Fe cu a
Ratio I V i V
I V + v, Mole R
0.5 4.5
11
3 2 5 3
13 13 14 19 30
9
70" C. at 2-atm. pressure. Ammoniaxitrile, 5:l in 2-propanol.
VOL. 8 NO. 2 JUNE 1 9 6 9
147
of ammonia, but this causes some deactivation. For ordinary metal catalysts the same effect is obtained with sodium carbonate or hydroxide. The deactivation caused by the sodium salts is very much greater than that caused by ammonia and so the latter is the preferred expedient. The deactivation in 2-propanol generally appears greater than in water. Walker and Maxted (1948) claim it to be due to the formation of the nontoxic ammonium ion; copper and iron borides are almost completely deactivated in 1.P.A.-ammonia solutions. An investigation of the effect of small quantities of foreign metals on rhodium and cobalt borides shows that, in general, selectivity is, if anything, decreased, and often is accompanied by deactivation. The least active metals cause smaller loss of selectivity, while platinum has the strongest influence, seriously altering the product spectrum. After completion of this work (November 1966), the hydrogenation of butyronitrile (Greenfield, 1967) was reported over similar metal catalysts, although not borides. Hydrogenation over borides was carried out under more severe temperatures and pressures. Nevertheless, the two sets of results are in fairly good agreement. Unsaturated amines are not readily obtained from acrylonitrile by hydrogenation over these metal and metal boride catalysts. Reduction of the olefinic linkage is more facile than reduction of the nitrile group and under mild conditions (30"C., 3 atm.) propionitrile is the major product. Propionitrile is the major product on hydrogenation over Raney nickel and copper metal catalysts (Reppe and Hoffman, 1932). The products of hydrogenation of acrylonitrile a t elevated temperatures are similar to those from propionitrile, as one might expect. Unsaturated nitriles, tallow nitriles in particular, have been hydrogenated to unsaturated amines over copperchromium oxide catalysts (Armour & Co., 1955). The products are, however, largely secondary amines, although the original work with this catalyst (Adkins, 1937) indicated that for nitrile reduction copper-chromium oxide was not a very satisfactory catalyst. The present work shows that acrylonitrile does not undergo facile C = C hydrogenation over copper-chromite, but is slowly hydrogenated to diallylamine. I n this work, the proportionate yield of primary amine is very much greater than with tallow nitrile, but even so it is small. The presence of ammonia in the reduction of acrylonitrile causes complications by adding across the C = C to form either CNCH2NH2 (IV) or (CKCH2CH2)2NH (V). The relative amounts of each are dependent on pressure, concentration of ammonia, and catalyst type. The former is more readily formed with higher concentrations of ammonia, and increase of pressure causes an increase in IV and V. With platinum boride, addition of ammonia to C = C is less than with other catalysts, and V is preferred to IV. On the other hand, all other catalysts show a greater preference for IV, in varying degrees, from nickel wholly IV, to rhodium 2 : l . The total amount of adduct formed is greatest with iron. A slight variation of activity and selectivity towards ammonia addition is found with variation of catalyst support and method of preparation, but it is too small for any pattern to be discerned. This suggests that we may be dealing with a statistic average throughout. Perhaps no real conclusions can be drawn 148
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
with regard to relative selectivities and activities towards ammonia addition, except that although catalyst selectivity to primary amines is enhanced by ammonia, an undesirable side effect is also introduced, which leads to over-all decreased yield of amines. In the hydrogenation of the anthracene-acrylonitrile adduct over rhodium, cobalt, nickel, ruthenium, iron, and copper boride catalysts supported on carbon, secondary and tertiary amines were not detected under the present conditions, but propionitrile, allylamine, and propylamine were formed in varying amounts. That no secondary and tertiary amines were detected suggests that all the acrylonitrile was used in forming an adduct and the propionitrile must be produced by hydrogenolysis of the adduct and probably not through thermal decomposition of the same. The hydrogenation is more rapid a t high pressures and temperatures, and hydrogenolysis is considerably reduced a t low temperatures, < 100"C., especially over nickel, cobalt, and rhodium borides. Allylamine is the major product, almost regardless of which catalyst is used. Nickel boride is the most active catalyst but is less selective than cobalt and rhodium borides. Cobalt boride appears slightly more selective initially, but rhodium boride appears to be the most selective when reaction had gone to completion. As with hydrogenation of saturated and unsaturated nitriles, ruthenium, iron, and copper borides are less effective. Much has been published on the mechanism of nitrile hydrogenation (Greenfield, 1967; Von Braun et al., 1923), and it is generally believed that reaction proceeds via an imine intermediate. The probable reaction path for the hydrogenation of the acrylonitrile-anthracene adduct (I) is stepwise hydrogenation via an imine (11) to the hydrogenated adduct (111), which is then decomposed, yielding the unsaturated amine and anthracene. c Ha I
H2 -b
n
m
The formation of propylamine is somewhat puzzling, since hydrogenation of propionitrile would be expected to yield secondary and tertiary amines, but none were detected. Hydrogenolysis of I1 is not to be expected. The absence of secondary and tertiary unsaturated amines may well be due to steric hinderance, preventing the addition of I11 to 11, and no intermediate of the type
RCH-NH-R'
I
NH?
a precursor of secondary amine (von Braun et al., 1923) therefore can be formed. literature Cited
Adkins, H., “Reactions of Hydrogen with Organic Compounds Over Copper-Chromium Oxide and Nickel Catalysts,” University of Wisconsin Press, Madison, Wis., p. 53, 1937. Alder, E., Marton, J., Acta Chem. Scand. 15, 357 (1961). Armour and Co., Brit. Patent 773,432 (May 9, 1955). Bruson, H . (to Resinous Products and Chemical Co.), U. S. Patent 2,287,510 (June 23, 1942). Brown, H. C., Brown, C. A,, J . A m . Chem. SOC.72, 3299 (1950). Carothers, W. H., Jones, G. A., J . A m . Chem. SOC.47, 3051 (1925); Ger. Patent Application I. 51,944 (1935). Greenfield, H., IND.ENG. CHEM.PROD.RES. DEVELOP. 6, 142 (1967). Grunfeld, M. (to Attorney General of U. S.),U. S.Patent 2,449,036 (Sept. 7, 1948). Hartung, W. H., J . Am. Chem. SOC.50, 3370 (1928). Hofer, L. J. E., Inorg. Chem. 3, 1783 (1964). Mowry, D. T., J . A m . Chem. SOC.69, 573 (1947). Paul, R., Buisson, P., Joseph, N., Ind. Eng. Chem. 44, 1006 (1952). Petrov, A. V., Freicllin, Likh, Sladkova, J. A., Volovin, V. M., Isu. Akad. iVauk SSSR, Otdel. Khim. Nauk 1960, 1878.
Polkovnikov, V. D., Isu. Adad. Nauk SSSR, Otdel. Khim. Nauk 1959, 1488. Reeve, W., Edreckson, W. H., J . Am. Chem. SOC.72, 3299 (1950). Reppe, W., Hoffman, U. (to I.G. Farbeindustrie), U. S. Patent 1,891,055 (Dec. 13, 1932). Rylander, P. N., Kaplan, J. G., U. S. Patent 3,117,172 (1964). Rylander, P. N., Steele, D. R., Englehard Ind. Tech. Bull. 5, 113 (1965). Schoegler, E. J., Adkins, H., J . A m . Chem. SOC.61, 3499 (1939). Slaugh, L. H., Magoon, E. F., J . Org. Chem. 27, 1037 (1962). Smith, G., Holm, L. A. (to Shell Development Co.), U.S. Patent, 2,761,883 (Sept. 4, 1956). Thonnert, P., Leafaut, P., Legra, C., Compt. Rend. 258, 5207 (1964). Von Braun, J., Blessing, G., Zobel, F., Ber. 56B, 1988 (1923). Walker, A. G., Maxted, E . B., J . Chem. SOC.1948, 1093. Winans, C. F. (to Wingfoot Corp.), U. S. Patent 2,334,140 (Nov. 9, 1942). Young, H. P., Christenson, C. W. (to Armour and Co.), U. S. Patent 2,287,219 (June 23, 1942) RECEIVED for review June 10, 1968 ACCEPTED January 13, 1969
SYNTHESIS AND CHARACTERIZATION OF CALCIUM ORTHOPLUMBATE (CaaPbO4) J E R N E J
J E R N E J C I C ,
S T E F A N
S K L E D A R , AND
J O Z E
S E N C A R
Chemical Institute Boris KidriE, Ljubljana, Yugoslavia l h e rate of calcium orthoplumbate formation (determined as quadrivalent lead and expressed as per cent of lead peroxide) was studied as a function of temperature, heating time, nature of calcium component, and the calcium-lead components ratio in the starting mixture. Wholly hydrated,lime (without additional moisture) is the most efficient source of calcium in the synthesis of calcium orthoplumbate, and the temperature range 700’ to 75OOC. is the most convenient. With a slight excess of calcium, the color characteristics of the product, measured photoelectrically, depend on the CaO/PbO ratio less than without excess calcium. The previous data are partly reiected, generally confirmed, and in some cases new data are presented.
As A COMPOUND,
caJcium orthoplumbate has been known for several decades. At the end of the last century, Kassner (1889, 1890a,c,d), synthesized the orthoplumbates of the alkaline earths and characterized the products obtained (1894a, 1895, 1899, 1900a). He proposed their direct application in the ceramics and glass industry, in match making, and in varnish production as oil oxidation accelerators and their indirect use in the technical gas industry as oxygen transfer agents, and for bleaching, coloring, and printing in technical products industries (1890b,e,f, 1891a,b,c, 1893a,b, 1898, 1900b). Some of these proposals were patented (Kassner, 189413; Kassner and Gebr. Schultz, 1894). Nevertheless, with numerous substitutes available,
Kassner’s proposals did not receive attention until World War 11, when substitution of calcium orthoplumbate for the red lead pigment in iron and steel protective coatings was proposed (Read, 1946). Assuming that quadrivalent lead is a carrier of the anticorrosive propeties of the red lead pigment (Pb total, 91%; PbOl, 34%), use of calcium orthoplumbate pigment should save considera.ble lead (Pb total, 59%; PbOz, 68%). Because of the wartime lead shortage and its versatility in numerous other fieldsnuclear techniques, accumulator lead plates, ceramics, and the glass industry-conservation of lead has remained important. Recently the advantages of coatings pigmented with calcium orthoplumbate, especially for marine services, have been confirmed (van Eijnsbergen, 1961; Read, 1950, VOL. 8 N O . 2 JUNE 1 9 6 9
149
