The Catalytic Effects of Polyethylene Glycols and Their Ethers on the Reimer-Tiemann Reaction

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  • Reimer-Tiemann反応におけるポリエチレングリコール類の添加効果

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In order to evaluate the catalytic effects of polyethylene glycols (PEG's) in the ReimerTiemann reaction, the reaction catalyzed by PEG's was compared that in the presence of their diethyl ethers (PEGDEE's) or monomethyl ethers (PEGMME's) (Table 1). The paraselectivity increased with increasing the average molecular weight of PEG's and their ethers except for PEGDEE's. The total yield of o-and p-hydroxybenzaldehyde based on a phenol decreased markedly by use of PEGDEE's.<BR>The para-selectivity was affe cted by not only the concentration of aqueous alkali (Fig.1)but also the molar ratio of allkali to the terminal hydroxyl groups of PEG's or PEGMME'S (Fig.3). The yield of p-isomer increased with increasing the concentration of aqueous KOH, while, that of o-isomer had the maximum value at the KOH concentration of ca.20 wt%(Fig.2).<BR>The terminal hydroxyl groups of PEG's and PEGMME's are important to cause a regioselective reaction. The reaction using PEG 600 under the conditions of CMOH/CP-OH>10 gave a gummous intermediate, and that using PEGMME 750 yielded an oily one. The isolated intermediates were liable to acid hydrolysis to afford a great majority of the para-substituted product (Table 3). The absence of carbonyl absorption in the IR spectra of these intermediates suggested strongly the formation of acetal ([1a]). These observations indicated that the reactive species attacking the para position of a phenoxide was not dichlorocarbene but [3], which was generated by the reaction of dichlorocarbene with the terminal hydroxyl groups of PEG's or PEGMME's. The intermediate carbene [3] having a bulky structure seemed to attack preferentially the para position of a phenoxide by the steric demands.

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1989 (6), 977-982, 1989-06-10

    The Chemical Society of Japan

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