[curiouscat]

In some references regarding drying agents CaCl2 is mentioned as unsuitable for drying ketones. Is there a reason why?

Have people successfully dried ketones with CaCl2?

[discodermolide]

I presume you may get acid catalysed enolisation and subsequent α-chlorination.

[curiouscat]

I presume you may get acid catalysed enolisation and subsequent α-chlorination.

Is that a credible worry? Say, at room temp & short contact times. e.g. 1 hour. I'm working with a high boiling (~130 C) ketone.

I tried it & didn't see any major peak changes on the GC. But I could have missed a minor product, or an overlapping peak or a water soluble aduct.

[discodermolide]

It may require readily enolisable ketones.
In your case it may not be a problem due to the short exposure. On your scale it may just be a very minor side product. Why not stress it out under some more forcing conditions and see what it takes. Then you will have a better idea of the system.

[orgopete]

I'm not sure what disco is referring to. If as suggested, it would be a method. I would wonder about the effectiveness of calcium chloride drying ketones more than it catalyzing reactions. It is difficult to find good conditions for acid catalyzed aldol condensations (presumably because the reactions become more complicated). If calcium chloride was an effective catalyst, I would expect this would have become a common reagent in textbooks by this time.

As I recall, someone had reported on the effectiveness of various reagents for drying solvents. Perhaps calcium chloride was mentioned. What I recall is molecular sieves was the most effective. It could reduce the water levels to the lowest parts per million in a given solvent (excluding chemical means like LAH stills).

[curiouscat]

Why not stress it out under some more forcing conditions and see what it takes. Then you will have a better idea of the system.

Good idea! Will do a test with longer times, higher temp. & more loading of CaCl2.

Right now my loading is pretty small. 5% (w/w) suffices.

[curiouscat]

I would wonder about the effectiveness of calcium chloride drying ketones more than it catalyzing reactions.

Why so? CaCl2 ,in general, seems to be commonly accepted as a drying agent. Is there anything special about ketones that'd make you doubt CaCl2's effectiveness for removing moisture?

It is difficult to find good conditions for acid catalyzed aldol condensations

Tangential, but ironically, we've been doing in my plant a quite satisfactory, acid catalyzed aldol condensation, at  scale (~100 tons a month) for a couple of years now.

As I recall, someone had reported on the effectiveness of various reagents for drying solvents. Perhaps calcium chloride was mentioned. What I recall is molecular sieves was the most effective.

Oh, that'd be good to read. On this forum? Have a link?

[discodermolide]

Have a look at this link:
http://link.springer.com/article/10.1007/s00706-011-0609-0#page-1

it refers to a 3 component Mannich type reaction catalysed by calcium chloride.

[orgopete]

I would wonder about the effectiveness of calcium chloride drying ketones more than it catalyzing reactions.

Why so? CaCl2 ,in general, seems to be commonly accepted as a drying agent. Is there anything special about ketones that'd make you doubt CaCl2's effectiveness for removing moisture?

I was replying to the original statement that CaCl2 was unsuitable for drying ketones. I don't know what was meant by unsuitable. I think you can add CaCl2 to acetone without any perceivable reaction. I am only surmising. The question is beyond my experience. Acetone is the only ketone solvent that I have experience with. Since it is water miscible, I would not have an expectation that I might mix it with water and later dry it with some reagent.

It is difficult to find good conditions for acid catalyzed aldol condensations

Tangential, but ironically, we've been doing in my plant a quite satisfactory, acid catalyzed aldol condensation, at  scale (~100 tons a month) for a couple of years now.

I found it quite difficult to find examples in textbooks. Most examples of aldol condensations are base catalyzed. Perhaps the textbooks haven't learned of such a successful example.

As I recall, someone had reported on the effectiveness of various reagents for drying solvents. Perhaps calcium chloride was mentioned. What I recall is molecular sieves was the most effective.

Oh, that'd be good to read. On this forum? Have a link?

Unfortunately, no. That was a long time ago when I was still in industry. I think it was in JOC.

[orgopete]

Have a look at this link:
http://link.springer.com/article/10.1007/s00706-011-0609-0#page-1

it refers to a 3 component Mannich type reaction catalysed by calcium chloride.

http://www.orgsyn.org/Content/pdfs/procedures/CV3P0305.pdf

Yeah, I don't know. A Mannich is just one more reaction that with a complicated mechanism. I thought CaCl just absorbed water. What do you think it is doing?