1,1,2,2,9,9,10,10-Octafluoro[2.2]paracyclophane, also known as Parylene AF4, is an important compound used to test theories of bonding, ring strain, and delta-electron interactions. It is also a precursor for the chemical vapor deposition (CVD) of thin film polymers (poly(p-xylene)). These poly(p-xylene) are well suited for use as conformal coatings in a wide range of applications in the electronics, semiconductor, automotive, and medical industries.

An important aspect of the synthesis of 1,1,2,2,9,9,10,10-Octafluoro[2.2]paracyclophane is that the reaction must be performed under highly dilute conditions. The most common approach is to generate a p-xylene intermediate, which then dimerizes to form the para-cycloarene, as shown in the general synthesis of AF4 in Scheme 1.

In such processes, high dilution conditions are often required to provide an optimal kinetic environment in which the unimolecular cyclization of the intermediate radical 3 can effectively compete with the unwanted bimolecular oligomerization reaction. Although gram quantities of AF4 were first prepared using the traditional high dilution method, this also hindered the large-scale scale-up of the process.

Now, researchers have found that 1,1,2,2,9,9,10,10-Octafluoro[2.2]paracyclophane can be synthesized without using high dilution techniques. The study found that heating a mixture of 4 equivalents of zinc powder and 0.35M p-bis(chlorodifluoromethyl)benzene in dimethylacetamide to 100°C can produce AF4 in 60% yield, accompanied by some obvious oligomeric byproducts, but almost no insoluble polymers are formed.

References:

[1] WILLIAM R. DOLBIER. A Novel, Non-High-Dilution Method for Preparation of 1,1,2,2,9,9,10,10-Octafluoro[2.2]paracyclophane[J]. Organic Letters, 2000, 2 13: 1867-1869. DOI:10.1021/ol005943f.