Chemical Engineering, California Institute of Technology, Pasadena, CA 91125.
Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
Proc Natl Acad Sci U S A. 2014 Jun 10;111(23):8363-7. doi: 10.1073/pnas.1408345111. Epub 2014 May 27.
Terephthalic acid (PTA), a monomer in the synthesis of polyethylene terephthalate (PET), is obtained by the oxidation of petroleum-derived p-xylene. There is significant interest in the synthesis of renewable, biomass-derived PTA. Here, routes to PTA starting from oxidized products of 5-hydroxymethylfurfural (HMF) that can be produced from biomass are reported. These routes involve Diels-Alder reactions with ethylene and avoid the hydrogenation of HMF to 2,5-dimethylfuran. Oxidized derivatives of HMF are reacted with ethylene over solid Lewis acid catalysts that do not contain strong Brønsted acids to synthesize intermediates of PTA and its equally important diester, dimethyl terephthalate (DMT). The partially oxidized HMF, 5-(hydroxymethyl)furoic acid (HMFA), is reacted with high pressure ethylene over a pure-silica molecular sieve containing framework tin (Sn-Beta) to produce the Diels-Alder dehydration product, 4-(hydroxymethyl)benzoic acid (HMBA), with 31% selectivity at 61% HMFA conversion after 6 h at 190 °C. If HMFA is protected with methanol to form methyl 5-(methoxymethyl)furan-2-carboxylate (MMFC), MMFC can react with ethylene in the presence of Sn-Beta for 2 h to produce methyl 4-(methoxymethyl)benzenecarboxylate (MMBC) with 46% selectivity at 28% MMFC conversion or in the presence of a pure-silica molecular sieve containing framework zirconium (Zr-Beta) for 6 h to produce MMBC with 81% selectivity at 26% MMFC conversion. HMBA and MMBC can then be oxidized to produce PTA and DMT, respectively. When Lewis acid containing mesoporous silica (MCM-41) and amorphous silica, or Brønsted acid containing zeolites (Al-Beta), are used as catalysts, a significant decrease in selectivity/yield of the Diels-Alder dehydration product is observed.
对苯二甲酸（PTA）是合成聚对苯二甲酸乙二醇酯（PET）的单体，由石油衍生的对二甲苯氧化得到。人们对合成可再生、源自生物质的 PTA 很感兴趣。在这里，报道了从可源自生物质的 5-羟甲基糠醛（HMF）的氧化产物开始合成 PTA 的路线。这些路线涉及与乙烯的 Diels-Alder 反应，并避免了 HMF 加氢为 2,5-二甲基呋喃。HMF 的氧化衍生物在不含强布朗斯台德酸的固体路易斯酸催化剂上与乙烯反应，以合成 PTA 及其同样重要的二酯、二甲基对苯二甲酸（DMT）的中间体。部分氧化的 HMF，5-（羟甲基）糠酸（HMFA），在含有骨架锡（Sn-Beta）的纯硅分子筛上与高压乙烯反应，生成 Diels-Alder 脱水产物 4-（羟甲基）苯甲酸（HMBA），在 190°C 下 6 小时反应后，HMFA 转化率为 61%，选择性为 31%。如果 HMFA 用甲醇保护形成 5-（甲氧基甲基）糠酸甲酯（MMFC），则 MMFC 可以在 Sn-Beta 存在下与乙烯反应 2 小时，以 28%的 MMFC 转化率生成 4-（甲氧基甲基）苯甲酸甲酯（MMBC），选择性为 46%，或者在含有骨架锆（Zr-Beta）的纯硅分子筛存在下反应 6 小时，以 26%的 MMFC 转化率生成 MMBC，选择性为 81%。然后，HMBA 和 MMBC 可以被氧化分别生成 PTA 和 DMT。当使用含介孔硅（MCM-41）和无定形硅的路易斯酸或含沸石（Al-Beta）的布朗斯台德酸作为催化剂时，Diels-Alder 脱水产物的选择性/收率会显著降低。
