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January 18, 2010
Volume 88, Number 3
pp. 2,4

January 18, 2010 Letters

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Chemical Safety: Trimethylsilylacetylene Explosion

We would like to report an explosion that occurred in our laboratory last year while performing an oxidative coupling of trimethylsilylacetylene (TMSA) in a Glaser-Hay reaction. The explosion ruptured the 2-L reaction flask and seriously injured a researcher.

This reaction has been routinely used in our and many other laboratories to prepare 1,4-bis(trimethylsilyl)butadiyne-1,3 on a large scale (>100 g), and no dangerous or unusual behavior was previously noted.

The procedure involves purging oxygen through a solution of TMSA in acetone in the presence of a copper(I) chloride:tetramethylethylenediamine complex catalyst at room temperature as described by Andrew B. Holmes et al. (Org. Syntheses 1993, Coll. Vol. 8, 63). The authors of the procedure recommend a safety shield as a general precaution while working with flammable materials in the atmosphere of oxygen, although no hazard was ever encountered. In this incident, the explosion occurred as soon as we started adding the solution of catalyst in acetone to the reaction.

We have consulted with the pioneer of this reaction (Allan S. Hay) and the submitting author of the procedure (Holmes) and considered various scenarios to explain the explosion. Ignition of acetone/TMSA vapor by the external sources was hardly possible as the flask was well sealed and the outgoing gases were passed through a dry-ice condenser (lowering the vapor pressure below the explosive concentration) and brought to the back side of the fume hood through a 1-meter hose.

The reaction temperature (5 ºC) was noted by the researcher a few seconds before the explosion, thus ruling out unexpected reaction exothermy. The autoignition of the vapor on a hot stirring adapter (possibly heated by rotation-induced friction) was refuted, because joint lubrication was checked before setting up the experiment, and it would have required achieving an unrealistic temperature of greater than 300 ºC. Also, the explosion occurred upon adding the first few drops of copper catalyst, which makes crystallization of the explosive intermediate—copper bis(trimethylsilylacetylide)—highly improbable.

We speculate that a discharge of static electricity between the syringe needle and the digital thermometer inside the flask is the most likely cause of this explosion. A digital thermometer connected to a stirring hot plate (IKA) was used in the reaction, and a plastic syringe with a long metal needle was introduced through the same neck. An induced static voltage on the syringe through friction from handling (often observed in Montreal winter indoors while walking or even simply sitting) could then cause a sufficient differential potential on the needle for a discharge spark to occur close to the metallic body of the digital thermometer. The oxygen-rich atmosphere lowers the ignition energy and makes even a weak spark sufficient to cause a fire.

The incident emphasizes once more the potential danger of mixing oxygen gas with flammable solvents or reagents. More important, introducing two conductors into a flask brings a risk of static electricity discharge between the conductors, which is dangerous whenever a flammable solvent is used without inert gas. As wired metal-gauge digital thermometers are used more often in synthetic practice, precautions must be taken to avoid their contact with other metallic (conducting) parts inside the reaction flasks.

Dmitrii F. Perepichka
Shehzad Jeeva

A Wary Crafter

I recently started sewing items from oilcloth, the material used in the 1950s and 1960s for picnic tablecloths and the like. As with so many other things from "the good old days," oilcloth is enjoying a renaissance among crafters. It is available in many patterns and colors from a number of online fabric stores as well as chain stores catering to those of us who enjoy sewing.

While innocently "surfing" among the many websites and blogs by and for people like me, I was amazed to find that there are some real concerns regarding the use of oilcloth for food-contact applications, especially its use for lunch bags. The problem seems to hinge upon the vinyl used to coat the cotton "web" that is printed with the pattern. Of course, the vinyl coating is the feature that makes oilcloth so attractive to use in lunch bags because it is moisture resistant. Children 12 and under are considered to be at the greatest risk—exactly the group most likely to use lunch bags!

Other fabrics, such as "laminated cotton," PUL (which I believe is an acronym for polyurethane laminates), and even rip-stop nylon are also suspected as being hazardous when used in direct contact with food. Built ( is a brand of very attractive neoprene-based lunch bags and other items. The company says neoprene is safe, but after reading your article on leachates from packaging I don't know what to think (C&EN, Aug. 31, 2009, page 11).

The underlying motive for sewing and using these articles for lunch bags is to minimize the millions of single-use plastic and paper bags used to package foods to take to school and work. As virtuous as it might be to limit disposables, however, I don't want to replace one hazard with another.

Would lining an oilcloth lunch bag would make it safe for use? Can these fabrics be used to sew aprons, placemats, and other products that are used with food, but not directly to package it?

I contacted the Department of Agriculture but was referred to the Food & Drug Administration because the USDA apparently is concerned "only" with the safety of the food itself (for example, Escherichia coli in meat) and not the packaging. I have yet to reach anyone at FDA.

Thanks in advance for any advice you can give me. I never would have expected my sewing hobby to lead to such concerns!

Opal Rosenfeld

Employment Of Chemists

I'm writing about the article "Shipping Drug R&D Abroad" (C&EN, Oct. 12, 2009, page 16). I'm 22, and I graduated from college in May and went straight on to graduate school. What upsets me is that I chose chemistry specifically with the hopes that one day I could work in drug R&D. I also chose science because I believed it was stable and actually quite beneficial. If I had known it would be like this, I would have just tried to become a pop star!

I'm worried about the future of R&D in the states, even if the professionals quoted in the article aren't. Given the bad economy, recession, layoffs, and now outsourcing, it seems like young adults don't have a chance.

Even if jobs were to become available, I'm quite certain we'd be at the end of everyone's list to interview. It seems painfully obvious to me and everyone I know: No one will hire us if we have no experience, and we can't get experience because no one will hire us.

Science is obviously the way of the future. If you have to go abroad to find R&D talent, doesn't that mean there isn't a talent pool in the U.S.? And if we have a talent pool of experienced R&D scientists, aren't inexperienced scientists going to falter and fall to the side? I fear that we'll fall behind in science because absolutely no opportunities are being offered.

When the outsourcing hype dies down, then what? We try again here? How can we be certain that we will have anyone qualified to do the work? When I graduate in two years, I don't think anything will have turned around. I just don't think anyone should be surprised in two, five, or 10 years when we need R&D in the U.S. and turnout is less than stellar.

Tisha Hutchinson
Piscataway, N.J.

M. Matelich really hit it in his letter, "Boys and Science Education" (C&EN, Sept. 28, 2009, page 7), which also confirmed the article titled "Vanishing Plants" the previous week (C&EN, Sept. 21, 2009, page 21). In it, we read that DuPont (Itypalon), Dow (Solution Vinyls), Celanese (formic acid), and Nova (SMA copolymers) have all closed plants that were domestic producers, leaving a number of chemists to join the unemployment ranks. In addition, supplies of those chemicals now have to be brought in from foreign sources. This goes along with the pharmaceutical industry slowly outsourcing R&D.

In the past 50 years, we've seen a slow erosion of U.S. manufacturing capacity and greater dependence on foreign suppliers. This leads to two questions: Will we really need any chemists in the future, and will the U.S. economy be able to survive to any major degree as an almost 100% service and almost 0% manufacturing economy?

We may well be entering an era when employment of chemists becomes a corporate luxury.

Bob Weiner
Northbrook, Ill.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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