quantitative results on drying different solvents with different desiccators.
many results are unpredictable and unambiguously show that one can not extrapolate drying ability of reagents for different solvents. for example, for meoh drying with ms 3a powder give much worse results than beads. at the same time, for etoh and t-buoh using powder gives substantially superior results. cah2 is very good for drying hmpa and benzene, but gives quite poor results for ch3cn and dmf.
conditions:
desiccant loading 5% w/v (5g/100ml)
stirring gives better results than static drying or even reflux (most likely due to breakdown of particle size).[1]
when using ms for dying: if you want to distill solvent afterwards, don’t distill it from ms.[2]
cah2 was freshly grounded [1]
ms were activated for >3h at 300-320°c or24h at 250°c (see dependence of activation temperature on capacity in this ref.) [2]
benzene [1]
[initial water content 100 ppm (0.01 % w/w)]
drying:
4a ms, al2o3, sio2, cah2, lialh4, na, cacl2: <1 ppm (for exact conditions see the ref.)
simple fractionation (after discarding the first 20%): 15 ppm
dioxane [1]
[initial water content 2300 ppm (0.23 % w/w)]
drying:
stirring with cah2 for 24h gives 4 ppm (reflux gives 14 ppm),
na-benzophenone becomes blue at 20 ppm of h2o,
na (24h reflux) leaves 5 ppm,
distillation from na-k alloy after static drying for 6h (22 ppm), 1day (11 ppm),
koh (ground), static drying for 7 days (14 ppm, 8 ppm after distillation)
ms 4a for 96h (13ppm) [2]
poor results: lialh4 (1 day: 900ppm), al2o3, sio2, cacl2, p2o5 (1 day: 400ppm)
acetonitrile [1]
[initial water content 2800 ppm (0.28 % w/w)]
drying:
p2o5, static drying for 24h , followed by distillation (12 ppm). distilled sample can be
slightly contaminated with p2o5-residue, subsequent distillation from k2co3 is recommended).
3a ms, static drying for 1 day (49 ppm), 7 days (27 ppm).
b2o3, static drying for 24h , followed by distillation (59 ppm). b2o3 is not volatile.
poor results: 4a ms (450ppm), cah2(1300ppm), koh, sio2, al2o3, caso4, cacl2.
hmpa [3]
[initial water content 2620 ppm (0.262 % w/w)]
drying:
distillation from p2o5 gives strongly colored solution, after distillation contains 22 ppm of water. this method is not recommended by authors.
the best method (on author’s opinion): distillation from cah2 (80 ppm) , followed by storage over 4a ms (29 ppm). another possibility is sequential drying for 72h over 4a ms (29 ppm).
poor results: koh, bao, al2o3, b2o3, na-k alloy (decompos.),
dmf [3]
[initial water content 2860 ppm (0.286 % w/w)]
drying:
sequential drying for 2x72h over 3a ms (1.5 ppm)
distillation from p2o5 (2 ppm).
poor results: b2o3; al2o3; dist. from koh (303ppm) or cah2 (94 ppm).
dmso [3]
[initial water content 2560 ppm (0.256 % w/w)]
drying:
initial fractional distillation (261 ppm) followed by sequential drying for 2x72h over ms 3a (10 ppm).
poor results: p2o5 (1.4 ppm, but contaminated by decomposition products).
acetone [3]
[initial water content 2890 ppm]
drying:
b2o3: stirred (24h?), distilled, and sequentially dried 2x24h (18 ppm)
poor results: ms 3a (6h: 115ppm, 72h: 322ppm) and ms4a (6h: 331ppm, 72h:1720ppm) after prolonged drying cause self-condensation and increase of water content; p2o5 (24h then dist.: 1970 ppm); cuso4; k2co3; caso4; bao
meoh[4]
[initial water content 1010 ppm]
drying: ms 3a (beads, not powder!) for 24h (95ppm); mg(5g/l)/i2 for 24h (97ppm); fist mg/i2, then ms 3a, 48h (12ppm).
poor results: ms 3a (powder), ms 4a beads (440ppm), cah2 (125ppm);
etoh[4]
[initial water content 1500 ppm]
drying: ms 3a (powder, not beads) for 24h (18ppm); mg(20g/l)/i2 for 24h (50ppm).
poor results: ms 3a beads (99ppm), ms 4a beads (400ppm), cah2 (99ppm);
2-buoh[4]
[initial water content 1000 ppm]
drying: ms 3a beads (24h: 645ppm; 96h: 9ppm); ms 3a powder (24h, 14 ppm); cah2 for 2h then dist. (17 ppm)
t-buoh[4]
[initial water content 1030 ppm]
drying: ms 3a powder (not beads!) for 24h (13 ppm); cah2 or na for 24h, the dist. (20 and 10 ppm corresp.);
poor results: ms 3a beads for 168h (160 ppm); ms 4a for 24h (406ppm)
1,2-ethanediol [4]
[initial water content 2700 ppm]
drying: benzene azeotrope (contamin. by 0.02% benzene, water content 65ppm);
poor results: ms 3a and 4a deads or powder (360 to 2000 ppm), mg/i2 (150 ppm)
2,3-butanediol[4]
[initial water content 4000 ppm]
drying: ms 3a powder for 6h (140 ppm).
pyridine[5]
[initial water content 2500 ppm]
static drying: cah2 or cac2 (24h: 39ppm; 168h 10ppm), ms 4a sequentially dried 2x24h (0.3ppm);
poor results: al2o3, na, koh (24h, 152ppm), benzene azeotrope, bao, etc.
2-methylpyridine[5]
[initial water content 2500 ppm]
drying: static over bao for 24h (27ppm), static over ms 3a for 24h (55ppm), benzene
azeotrope (40ppm);
poor results: cah2 and cac2 (70-80ppm), koh, etc.
2,6-dimethylpyridine[5]
[initial water content 2500 ppm]
static drying : cah2 or ms 3a or 4a (24h: ca. 220ppm; 168h: ca 130ppm);
poor results: koh (325ppm), benzene azeotrope (207), bao etc.
2,4,6-trimethylpyridine[5]
[initial water content 2500 ppm]
static drying for 24h: cac2 (8 ppm), koh powder (27ppm), bao (33ppm), ms 3a (47ppm);
poor results: cah2 (132 ppm), benzene azeotrope.
triethylamine[5]
[initial water content 2500 ppm]
static drying: ms 3a or 4a for 24h (ca 33ppm), koh powder (24h: 37ppm, 168h: 23mm),
cah2 (24h: 68ppm; 168h: 34ppm);
poor results: na, al2o3, bao etc.
diisopropyethylamine[5]
[initial water content 2500 ppm]
drying for 24h: na(stir) or cac2(stir) or static ms 3a or 4a (<25ppm).
poor results: cah2 (stirred for 24h: 150ppm).
1,3-propanediamine[5]
[initial water content 2500 ppm]
drying for 24h: cac2 stir (<25ppm), static ms 3a or 4a (<25ppm);
poor results: cah2 (500ppm), na, bao;
