The purpose of the patent was to synthesize and evaluate reactive monomers containing phosphorous useful as flame retardants in applications such as printed circuit boards.
Three consecutive O-alkylations were performed in one pot using 3.0 equiv NaOH for the reactions shown using tri(hydroxyphenyl)ethane as the substrate (Example 2 in the patent). In the first etherification, three phenolic OH’s are available for deprotonation, so no excess of hydroxide was needed given the pKa of the phenol of 9.
The patent did not report a yield, so it is not known how much of the second reactant containing phosphorous (DOPO-HQ potassium salt), reacted at both ends since free chloromethyl groups are present before complete conversion and could conceivably be etherified. In fact, when etherifying unsubstituted hydroquinone with an alkylating agent in the presence of a phase-transfer catalyst, the dominant product is the diether since the phase-transfer catalyst quat stays paired with the more organophilic ether-monoanion than with the as-yet non-etherified hydroquinone dianion. That encourages dietherification over monoetherification. Obviously, the inventors made enough of the desired material to proceed to the third etherification.
In the third etherification, with VBC, the phase-transfer catalyst quat replaces the potassium as the cation and the reaction proceeds.
In Example 3 of the patent, the substrate was tetra(hydroxyphenyl)ethane and they used 4.0 equiv NaOH.
Additional examples that used TBAB reacted non-phosphorous monomers such as diallyl bisphenol A or performed only two etherifications.
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