|MadSci Network: Chemistry|
Hi Jack, I'm sorry I don't have a good answer for you. I did not find anything connecting the use of linseed oil and cyclopentadiene. Here is what I do know that might help you out some. Cyclopentadiene is a five carbon cyclic hydrocarbon containing two double bonds in conjugation. This arrangement makes it an excellent Diels-Alder diene and it readily reacts with itself at room temperature to form a dimeric species aptly called dicyclopentadiene (a crystalline solid with mp=32 degrees C). A bottle of cyclopentadiene left standing will be completely dimerized in a few days. Cyclopentadiene may be recovered by heating the dimer to >150 degrees C causing the retro-Diels Alder to occur then distilling off the monomeric cyclopentadiene (bp is around 30 degrees C I think) into a cooled receiver flask. Material obtained in this way may be used as cyclopentadiene for a day or so before significant amounts of dimer form. So my first answer to your question is that cyclopentadiene is probably _not_ used for the purpose you described because it is simply not practical. If it is used then it is probably used in the dimeric form. In any case I cannot see how it would facilitate drying of linseed oil and I was unable to find any reference to it. Linseed oil is obtained from linseeds, constituting 30-40 percent of the total mass. The oil contains a mixture of glycerides of unsaturated acids: linolenic, linoleic, oleic, stearic, palmitic, myristic. [Merck Index, 8th ed.] The oil dries by air oxidation to solid (or viscous) products. I can guess that if linseed oil was treated with cyclopentadiene (in the monomeric form only) then Diels-Alder reaction would occur between the double bonds in the unsaturated oils and the two double bonds in the cyclopentadiene. The norbornene-like products would likely be solids and therefore would not need to be oxidized in order to "dry"; however, this is only an unsubstantiated guess. Well, I hope some of this information was helpful! Jeremy. DIELS-ALDER REACTION WITH CYCLOPENTADIENE: HC-CH R R HC=CH // \\ | | ------> / \ HC CH + HC=CH <------ HC-CH2-CH \ / \ / CH2 HC-CH | | Cyclopentadiene alkene R R Norbornene-like structure
Try the links in the MadSci Library for more information on Chemistry.