86
Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 86-91
The combustion to CO + C02 seems to run parallel to the ratio 02/HC1 in the feed. In order to obtain high yields of perchloroethylene, Le., high degrees of chlorination, it is necessary to use a feed mixture richer in HC1+ O2 than calculated from eq 1 and 2. We have postulated a reaction scheme which accounts reasonably well for all the reaction products observed. Finally, we have also shown that, with the exception of C C 4 , the chlorinated byproducts can be recycled without accumulating in the reactor. Literature Cited Arcoya. A., cort~s,A,, Seoane, X. L., Ind. Eng. Chem. Prod. Res. Dev,, preceding article in this issue, 1980.
Atasov, A. A., Kartasov, L. M., Treser. Y. A,, Sharinova, L. M., Zh. Prikl. Khim., 48, 247 (1975). Bellis, H. E., Belgian Patent 614589 (Sept 3, 1962). Bohl, L. E., Vancamp, R. M., French Patent 1357 453 (April 3, 1964). Kawaguchi, T., %to, K., Tanaka, K., Japanese Patent 7601 681 (Jan 20, 1976). Knoop, J. F.. Neikirk, G. R., Hydrocarbon Process., 109 (Nov 1972). McColl, I. S., British Patent 1412336 (Nov 5, 1975). Miller, S. A., Chem. Process Eng., 47, 268 (1966). Yamaguchi, T.. Sato. N., Tanaka, K., Japanese Patent 7407 130 (Feb 19. 1974).
Received f o r review July 24, 1979 Accepted December 4, 1979 We are grateful to CROS, S.A. for financial support to carry out this work.
GENERAL ARTICLES The Preparation and Cation Complexation Properties of Macrocyclic Polyether-Diester Ligands: A Short Review Jerald S. Bradshaw,' R. Elliott Asay, Steven L. Baxter, Paul E. Fore, Scott T. Jolley, John D. Lamb, Garren E. Maas, Michael D. Thompson, Reed M. Izatt, and James J. Christensen Chemistry Department and Contribution No. 192 from the Thermochemical Institute, Brigham Young University, Provo, Utah 84602
The synthesis and complexation properties of a series of macrocyclic polyether-diester ligands are reviewed. Over 70 compounds are listed. Cation complexation properties were studied by temperature dependent 'H NMR spectroscopy, calorimetric titrations, and membrane transport of metal cations. In general, the macrocyclic polyether-diester compounds are not as good at complexing metal cations as are the polyether crown compounds. The diesters containing a pyridine subcyclic unit, which complex very strongly with all cations studied, are an exception to the general rule stated above. The temperature dependent 'H NMR spectral results show that macrocyclic polyether-diester ligands containing furan and benzene subcyclic units have a different complex stability order with benzylammonium perchlorate than do the pyridine-containing ligands. With the pyridino ligands, complexes with the 18-membered ring were the most stable. On the other hand, for the benzo or furano ligands, the 24membered ring compounds form more stable complexes than those with smaller macrorings.
Introduction The macrocyclic oligomers of ethylene oxide (crown compounds) have received considerable attention in recent years because of their ability to complex metal cations selectively. Pedersen was the first to study systematically the synthesis and unique cation complexation properties of the crown compounds (Pedersen, 1967,1972). Since the IUPAC names of the macrocyclic polyethers are difficult to use, Pedersen developed a trivial nomenclature system. The trivial name consists of (1) the number and kinds of substituents, (2) the total number of atoms in the cyclic polyether ring, (3) the class name, crown, and (4) the number of oxygen atoms in the ring (Pedersen, 1967). Thus the trivial name for compound 1 is dicyclohexano18-crown-6. The preparation and properties of the crown T
o
compounds has been the subject of a number of recent reviews (Christensen et al., 1974; Gokel and Durst, 1976; Weber and Gokel, 1977; Izatt and Christensen, 1978; Melson, 1979). We have prepared a wide variety of macrocyclic polyether-diester compounds which are closely related to the crown ethers (i.e., compare compound 2 and its diketo derivative shown below). Macrocyclic diesters can be
2
1
(37: Cod 1
0196-4321/80/1219-0086$01.00/0
considered as keto-substituted crown compounds. This review describes the synthesis of the macrocyclic polyether-diester ligands and their cation complexation properties. 8 1980 American
Chemical Society
e7
d
rl
B
Lbnd
s
Figure 1. Proton NMR spectra for 108 and for the complex ot 1Od with isopropylammonium perchlorate at room temperature,-70, -30, -10 O C (coaleecencetemperature) and at +a0 O C in CD& (solvent peak at 5.25).
11112
$ y ~ ~ ~ e ~ i $ The macrocyclic polyether-diester ligands can be prepared by a variety of methods. Although essentially ail of the early synthetic work on macrocyclic diester comgbounds involved the reaction of dibasic acids or esters and glycols (Bradshaw et id.,1979b), none of the macrocyclic dieater ligands reported in this review has been so prepared. The moat hquer!tly used method has been the reaction of a diacid chloride with various glycoirr (eq 1)
X,Y =CH.N
nzZ.5
I
In
(Bradshaw et ai., 1970,1978; Bradshaw and Thompson, 1978; Maaa et al,, 1977). Treatment of the salt of certain dibasic acids with an dkyl dihalide hrns also been ueed to make a A w of these mcrocyciic compounds (Piepers and Kellogg, 1978; a and Kellogg, 1979; Drewes and Ripwen, 1974). ting to note that the acyclic palymter byproduct from some of these reactions can be depolymerized to the lmacroryclic 1:l diester compound by heating the polymer with various metd salts (Spanagel and Carothers, 1936; Fore et d.,1978). B listing of the synthetic macrocyclic poly. campounds (84% FXXChart I) prepared from leae &cola. Some of theae compounds have n complexing abilities; however, the comproperties of moat have not been tested. No ing compounds are lietsd in Table I and pyridino ligands 10-12 ate the only nitrogen-containing compounds, A complete listing of all t p of macrocyclic di- and tetraaabr compounds is given in a recent review rdshrw e t J.,1W9b).
ic 1 of some of these rm bchniques: temperaopy, calorimetric ti. rt of metal cationa.
NMR 8pectmrcopy, by clertain of the Uganda 9,10, and
6ol-d/
x:
CI
H
=h
SUBSTlTUEM
Filum 2. Free energies of activation (AG:, kcal/mol) for the diesociation of complexes of tcrt-butyl- and benzykmmonium dta with pyridino ligmds 10 vs. the subtituent.
13 with primary alkyiammonium cations in methylene chloridsD2 was accompanied by significant chemical Bhift changee in the 'HhMR epectrat (we Figure 1for axample) (Bradshaw et al., 1979a,c), A study of the temperature dependenciee of the 'HN M R spectra for thm complexeta provides the information needed to d c d a t e the freta encomplex ergy of activation ( (Sutherhd, 1971; rd et aL, 1978). These A&' values are a measure of the kinetic stabilitie8 of the complexes. Thus, the e f l h of aubstit uenb, ring eize, and subcyclic units on liiand-alkylammonium cation complexation can be studied. In every system studied except the P I - m ~ d ~ n em dl e roring containing pyridine, the methory eubtituent en= h a n d the kinetic atability of the complex WU uls chlm or nitro substituent d e e d the kinetic atabillty (em F m 2 cand 3). This kinetic atabllity ordrar padeb the electronic donating effwt of the methoxy group aad ttae withdrawing effects of the &m and nitro plexen of benqhmmonium per& ligands (10) show a dinemat kinetic mcrcrorins s h than t h m with tbe benro 6 oc furam (18) subcyclic units. In the cnae of the p y r i b &a of am= pounds, complexes with the l & m m Mring ugradr,M
88
Ind. Eng. Chern. Prod. Res. Dev., Vol. 19, No. 1, 1980
Table I. Synthetic Macrocyclic Polyether-Diester Ligands coml)ounda
3
3 4
4
2
3 3 3 4 4 4 4 5
2
3 3 3 4 6
7
8
3 3 3 4
2 2
3 3 3 3 3
4 4 4
10
4a
51.5-52.5 67-68 (1A6-14810.17) 83.5-85 65-66 (176-18210.6) ( 198-203/1.3) 69-70
34 27 28 28 38 35 34
57-58
..
g
18
d d
5a 5b 5c 5d 5e
R=X= H
6a
-H = CH, = C,H, -H = CH, = C,H, = n-C,H,, = 1',2'-cyclohexano (syn) (anti) R=H R - CH, R = C,H,
R'=H
R =X = H
NO,, R ' = H R'= H NO2, R' = H H, R' = NO2 R'= H NO,, R' = H R S R' = H R = NO,, R ' = H
R= R= R= R= RR= R= R= R= R= R=
6 6
CH,, X = H C,H,, X = H X = E1 H, X = C1 H, X = OCH, CH,, X = H C,H,, X = H X=H H, X = Cl H, X = OCH, CH,, X = H R=X = H R = H, X = C1 R = H, X = OCH, R = II,X = C1 R = H, X = OCH,
2 2 3 3 4 5
m=l,R=H m = 1, R = CH, m = 1, R = H m = 1, R - CH, m=l,R=H ?n=l,R=H
0 1 2 3
m = 2,R = CH, m = 2, R = CH, m = 2,R = CH, m = 2,K = CH,
ref
28 55
= H -H = CH, = C6Hs =H
R R R R R R R R
yield
45-46 84-85
R R R R R
R = X- F R = CH,, X = H R= X= H
mP @PI, "C
3a 3b 4b 4c 4d 4e 4f 4g 4h
2 2 2 3 3 3 3 3 4 4 4
5
no.
H H C,H, C,H, H C,H, n-C,H!, R = C,H,
R= R= R= R= R= R= R=
5
12
R= R= R= R= R = R= R=
2 2 3 3 3 4 4 5 5
4 5
11
_______
1 2 3 2
9
su bstituent s
n
liquid
C
C
d d c,
f
e
f
f
liquid
(146-154/0.2)
b b
C 1
30-31
C
d d d
6c 6d
(155-15710.65) (135-14310.3) ( 130-14210.12) li cl u i d
31 23 37
7a 7b 7c
57-58 (154-155/0.7)
31 20
h d , g, i d
100.5-101.5 116-117 102.5-104 78.5-79.5 (170-17211) 61-63 68.5-69
26
g
6b
8a
8b 8c 8d 8e 8f 8g
8h 8i 8j
8k 81
Ya
9b 9C Yd 3e 9f dg
9h 9i
liquid
50-51
12a
196-198
l%b 12c
...
12d
32 46 35
2 3 33 17
137-137 5 167-169 112-113 90-92 54.5-55.5
1l e llf
f
138-140 161-163 95.5-96 157-158 124-126 103.5-104.5 104-105 106.5-108.5 YO-92
lla lld
k
13
23
139-140 (16511) (17011.5) 86.5187.5 104-105 116-117 81-83 103.5-105.6 143-144.5 70-71 122-123 (17511) 110-111 65-66 7 2-73 52-53
llc
3
180-181 124.5-126.5 (20010.2) (172-17510.8) (188-19013)
10a 10b 1oc 10d 1 Oe 10f log 10h 1 Oi lOj 10k 101 10m 10n 100 1OP 1oq
llb
C
j k
f f
26 45 34
28 30 31 6
10 10 31 78 91 54 19 3 25 71 19 41 29 38 43 45 37 1
..
33
..
7
8
..
1, m, n
1 m 1 1 1
Ind. Eng. Chern. Prod. Res. Dev., Vol. 19, No. 1, 1980
89
Table I ( C o n t i n u e d )
n
compound'
substituents
X= X= X= X= X= X=
3 3 4 4 5 5
13
no. 13a 13b 13c 13d 13e 13f
H OCH, H OCH, H OCH,
mP "C 117-118 167-167.5 133-134 84-85 93.5-95 67-67.5
yield 60 67 27 31 30 14
ref
t t t t
t t
a See Chart I for structure of the compounds. Fore et al. (1978). Bradshaw e t al. ( 1 9 7 6 ) . Thompson et al. Arbuzov and Vinogradova ( 1 9 5 2 ) . Shimanskii et al. ( 1 9 7 7 ) . e Izatt et al. (1977a). f Bradshaw e t al. ( 1 9 7 9 e ) . Bradshaw and Jolley (1979). Bradshaw and ( 1 9 6 5 ) . Spanagel and Carothers ( 1 9 3 5 ) . .I Maas e t al. ( 1 9 7 7 ) . Thompson ( 1 9 7 8 ) . F r e n s c h a n d Vogtle ( 1 9 7 7 ) . Piepers and Kellog ( 1 9 7 8 ) . Bradshaw e t al. ( 1 9 7 8 ) . P Bradshaw van Bergen and Kellog ( 1 9 7 6 ) . van Bergen and Kellog ( 1 9 7 7 ) . et al. (1979a). 4 Bradshaw e t al. (1980). Bradshaw e t al. ( 1 9 7 9 ~ ) .
'
'
M'+L-ML' (Methanol)
n=5 13e-4
-
p ,
6.0 8'o]
18-Crown-6
131
13d
13c
n:5 -/9h
-
9i 13a
Na'
K'
Figure 5. Thermodynamic selectivity (as given by log K values in methanol at 25 "C) between Na+ and Kt of valinomycin, 18-crown-6 and 2,6-diketo-18-crown-6. X=
NO2
H
OCHs
Figure 3. Free energies of activation (AG: kcal/mol) for the dissociation of benzylammonium perchlorate complexes of furano (13) and benzo (9) ligands vs. the substituent. 5.e cs+ r Log K
(MeOH 250c
Na+? 4.0-
' \
3.0
1
2.0-
13
Y
Figure 6. Variation of log K values (methanol, 25 "C) for metal ion complexation between a crown ether (18-crown-6)and its 2,6-diketo substituted analogue.
.
1 '
1 18
21
I 24
Figure 4. Free energies of activation (AG:, kcal/mol) for the dissociation of benzyl- and tert -butylammonium perchlorate complexes of pyridino (lo),furano (13),and benzo (9) ligands vs. the macroring size.
the most stable. On the other hand, for the benzo and furano series of ligands, the 24-membered ring compounds form more stable complexes than those with smaller macrorings (see Figure 4). Since the benzene ring of
compounds 9 does not provide a heteroatom for the macroring and the furan oxygen which is part of the macroring for compounds 13 is a weak hydrogen bond acceptor (Timko et al., 19771, complexation with benzo and furano ligands (9 and 13) would take place in the oligoethylene oxide portion of the molecule. The larger macrorings with more ethylene oxide oxygen atoms would be expected to complex more strongly. The pyridino ligands, 10, on the other hand, would be expected to complex with alkylammonium salts through a hydrogen bond to the pyridine nitrogen. In this case complexing ability should fall off for the larger rings. Calorimetric Titrations. The results of thermometric titration experiments to investigate the reactions in
90
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 1, 1980
*
I
18-Crown4
~
60 Log K
1
\\
K*
Ba2' Cation
Figure 7. Thermodynamic selectivity (as given by log K values in methanol, 25 "C) between K' and Ba2+ of several macrocyclic ligands.
7ot
M'
- L-ML
Na
K
Rb
b
Figure 9. Rates of alkali metal transport through a chloroform membrane containing 1 mM 18-crown-6 or one of three substituted pyridino ligands.
-
75
LI'
10
Na'
125
15
K' Ab*
175 Cs*
Metal Ion Radius
270
n
L
Figure 8. Thermodynamic selectivity (as given by log K values in methanol at 25 "C) of three macrocyclic ligands among alkali metal cations.
methanol of the alkali and alkaline earth cations with a number of macrocyclic polyether-diester ligands and related crown ethers (Lamb et al., 1980a,b) and valinomycin are shown in Figures 5-8. The procedure used for these determinations has been described (Izatt et al., 1976). Several interesting results are noted in these data. First, a significant drop in cation-ligand complex stability was observed when the diketo groups were added to 18-crown-6 (see Figures 5 and 6). The metal cation selectivity of 18-crown-6 for Ba2+over K+ was retained for the diketo compound. A different metal cation selectivity (K' > Ba2+)was observed for the macrocyclic diester compounds with the malonyl, succinyl, and glutaryl moieties (Figure 7). In this latter case, even though complex stability was diminished, the cation selectivity shown by these ligand for K+ over Ba2+was similar to that found for valinomycin (Izatt et al., 1977a). A pyridino-18-crown-6 compound prepared by Cram and eo-workers (Newcomb et al., 1977) formed complexes with the alkali metal cations with stabilities much the same as with 18-crown-6 (Figure 8) (Izatt, et al., 1977b). Our comparable diester compound (10d) also is an excellent complexing agent for sodium, potassium, and rubidium ions although the selectivity for potassium over the other ions is somewhat diminished (Figure 8). Even with this diminished selectivity, compound 10d and related compounds 10e and 10f may be the most important of the new macrocyclic ligands because of the ease of their preparation (see Table I) (Bradshaw et al., 1980). Cation Transport Through a Liquid Membrane. The rates of transport of metal nitrate salts through a chloroform membrane containing some of the pyridino diester ligands, 10, was carried out as previously described
Na
K
18-Cr-6
Rb
CS
Figure 10. Transport selectivity among alkali metal cations of the macrocyclic carriers (1 mM) 78-crown-6 and three pyridino ligands of differing ring size.
(Christensen et al., 1978). As shown in Figure 9, the transport rates for potassium nitrate through the membrane with the substituted pyridino diester ligands containing 18 ring members was significant and decreased in the order: OCHB> H > C1. The methoxy-substituted ligand was particularly effective in transporting potassium nitrate. As one might expect, the larger methoxy-substituted 21-membered ring ligand (1Ok) transported rubidium
Ind. Eng. Chem. Prod. Res. Dev. 1980, 79, 91-97
nitrate the best of the pyridino diester compounds while the 24-membered ring ligand (100) was the best for cesium nitrate (Figure 10). The pyridino ligands (lOd,e,f,k,o) were all effective as carriers for silver nitrate (the rates of transport ranging frorn 312 to 770 mol X 10-7/h). Summary
A number of macrocyclic polyether-diester compounds have been prepared. Some of these new compounds complex with alkali and alkaline earth cations and alkylammonium ions. The macrocyclic compounds containing the pyridine subcyclic group are particularly good cation complexing agents and they are relatively easy to prepare. Acknowledgment
This work was supported by National Science Foundation Grant CHE76-10991 and Department of Energy Contract No. ER-78-S-02-5016.AOO (membrane transport experiments). Literature Cited Arbuzov, 8. A., Vinogradova. V. S., Izv. Akad. Nauk SSSR, Otd. Kbim. Nauk, 865 (1952); Cbem. Abstr., 47, 140584(1953). Beckford. H. F.. King, R. M., Stoddardt, J. F., Newton, R. F., Tetrabedron Left, 171 (1978). Bradshaw, J. S.,Bishop, C. T., Nielsen, S. F., Asay. R. E., Masihdas, D. R. K., Flanders, E. D., Hansen, L. D.,Izatt, R. M., Christensen, J. J., J . Cbem. SOC., ferkin Trans. 1 , 2505 (1976). Bradshaw, J. S., Thompson, M. D., J . Org. Cbem., 43, 2456 (1978). Bradshaw, J. S.,Asay, R. E.. Maas, G. E., Izatt, R. M., Christensen, J. J., J . Heterocycl. Cbem., 15, 825 (1978). Bradshaw, J. S.,Jolley, S. T., J . Heterocycl. Cbem., 16, 1157 (1979). Bradshaw, J. S.,Maas, G. E., Izatt, R. M., Lamb, J. D., Christensen, J. J., Tetrahedron Left., 635 (1979a). Bradshaw, J. S.,Maas, G. E., izatt, R. M., Christensen, J. J., Cbem. Rev., 79, 37 (1979b). Bradshaw, J. S.,Baxter, S. L., Scott, D. C., Lamb, J. D.,Izatt, R. M., Christensen, J. J., Tetrahedron Len., 3383 ( 1 9 7 9 ~ ) . Bradshaw, J. S.,Maas. G. E., Lamb, J. D., Izatt, R. M., Christensen, J. J., J . Am. Cbem. Soc., 102, 467 (1980). Bradshaw, J. S.,Jones, 6. A., Cragun, J. R., Jolley, S. T., unpublished data, 1979e. Christensen, J. J., Eatough. D. J., Izatt, R. M., Cbem. Rev., 74, 351 (1974). Christensen, J. J., Lamb, J. D., Izatt. S. R., Starr. S. E., Weed, G. C., Astin, M. S., Stitt, 8. D., Izatt, R . M., J . Am. Cbem. SOC., 100, 3219 (1978).
91
Drewes, S. E., Riphagen, B. G., J . Cbem. SOC.,ferkin Trans. 1 , 1908 (1974). Fore, P. E., Bradshaw, J. S., Nielsen, S. F., J . Heterocycl. Cbem., 15, 269 ( 1978). Frensch, K., Vogtle, F., Tetrahedron L e f t , 2573 (1977). Gokel, G. W., Durst, H. D., Synthesis, 168 (1976). Hodkinson, L. C., Leigh, S. J., Sutherland, I. O., J . Cbem. SOC., Cbem. Commun., 639 (1976). Izatt, R. M., Terry, R. E., Nelson, D. P., Chan. Y., Eatough, D. J., Bradshaw, J. S.,Hansen, L. D., Christensen, J. J., J . Am. Cbem. SOC.,98, 7626 119761. I , Izatt, R. M., Lamb, J. D., Maas, G. E., Asay, R. E., Bradshaw, J. S.,Christensen, J. J., J . Am. Cbem. SOC., 99, 2365 (1977a). Izatt, R. M., Lamb, J. D., Asay, R. E., Maas, G. E., Bradshaw, J. S., Christensen, J. J., Moore, S. S., J . Am. Cbem.,,Soc..99, 6134 (1979b). Izatt, R. M., Christensen, J. J., Synthetic Multidentate Macrocyclic Compounds", Academic Press, New York, N.Y., 1978. Kruizinga, W. H., Kellogg, R. M., J . Cbem. SOC., Cbem. Commun., 286 (1979). Lamb. J. D., Izatt. R. M., Swain, C. S., Bradshaw, J. S., Christensen, J. J., J . Am. Cbem. SOC., 102, 479 (1980). Lamb, J. D., Izatt, R. M., Swain, C. S., Christensen, J. J., J. Am. Cbem. SOC., 102, 475 (1980). Maas, G. E., Bradshaw, J. S., Izatt, R. M., Christensen, J. J., J . Org. Cbem., 42. (19771. .-, 3937 .._ Melson, G. A.' "TheCoordination Chemistry of Macrocyclic Compounds", Plenum Pubi. Corp., New York, N.Y., 1979. Newcomb, M., Timko, J. M., Walba. D. M., Cram, D. J., J , Am. Cbem. Soc., 99, 6392 (1977). Pedersen, C. J., J . Am. Cbem. Soc., 69, 7017 (1967). Pedersen, C. J., U.S. Patent 3687978 (Aug. 29, 1972). Piepers, O.,Kellogg, R. M., J . Cbem. SOC., Cbem. Commun., 383 (1978). Shirnanskii, V. M.. Gaevskii, A. F., Shkolnik, S. I., Gordinskii, 8. Yu, USSR Patent 176403 (Nov. 2, 1965); Cbem. Abstr., 64, 11340a (1966). Spanagel, E W., Carothers, W. H., J . Am. Cbem. SOC., 57, 929 (1935). Sutheriand, I.O., Ann. Rev. NMR Spectrosc., 4, 71 (1971). Thompson, M. D.. Bradshaw, J. S.,Nielsen, S. F., Bishop, C. T., Cox, F. T., Fore, P. E., Maas, G. E., Izatt, R. M., Christensen, J. J., Tetrahedron, 33, 3317 (1977). Timko, J. M., Moore, S. S.,Walba, D. M., Hibberty, P. C., Cram, D. J., J . Am. Cbem. SOC.,99, 4207 (1977). van Bergen, T. J., Kellogg. R. M., J . Cbem. SOC., Cbem. Commun., 964 11976)
van Bergen, T. J., Keliogg, R. M., J . Am. Cbem. Soc., 99, 3882 (1977). Weber, W. P., Gokei, G. W., "Phase Transfer Catalysis in Organic Synthesis", Springer-Verlag, Berlin-Heidelberg, 1977.
Received for revieu October 10, 1979 Accepted November 13, 1979 Presented a t the 34th Northwest Regional Meeting of the American Chemical Society, Richland, WA, June 13-15, 1979.
Stable Bubble Sensitized Gel Slurry Explosives K. Keirstead' and D. De Kee Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, Ontario, K7L 2 W3, Canada
Controlled stirring of ammonium nitrate gels in the presence of a lignosulfonate surfactant has been used to prepare gas emulsions of selected density. The gas emulsions function as matrices for the preparation of bubble sensitized gel slurry explosives. An experimental factorial design technique was used to relate three process parameters to the bubble density. The parameters are pH, the surfactant concentration, and the guar concentration. A photographic method was used to measure bubble size distributions after 24 h and after 30 days in the cross-linked gels. Data on aeration time and gel rigidity are also reported. So far (after 30 days), the results show that two samples, one at pH 4.3 and one at pH 6.0, favor a "good" bubble size distribution.
Introduction
The stability of foams formed from an aqueous solution of surfactants has been the subject of considerable interest for a number of years (Kumar and Kuloor, 1970). The stability of gas-liquid dispersions in viscous media has, however, received much less attention. Gas emulsions in high viscosity ammonium nitrate gels are important in the commercial preparation of bubble sensitized gelled slurry blasting agents. Ammonium nitrate 0196-4321 / 8 0 / 1 2 1 9 - 0 0 9 1$01 .OO/O
gels now used extensively in rock mining are quite insensitive to shock and are commonly sensitized either by the addition of self-explosives or by incorporation of air bubbles (Cook, 1968). Both the rate of detonation and the sensitivity to shock of ammonium nitrate gels may be controlled by the total volume and bubble size distribution of the air introduced. Bubble-rise due to the initial or subsequent formation of large bubbles will change both the density and the detonation sensitivity of the slurry. 0 1980
American Chemical Society
