CN102597328B - 改良的银阴极活化 - Google Patents
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Abstract
卤化的4-氨基吡啶甲酸的选择性电化学还原通过在+1.0至+1.8伏特的最终电势活化阴极而改善。
Description
美国专利4,217,185、4,242,183和6,352,635B2和美国专利申请公开2009/0090639描述了通过选择性电化学还原相应高级卤化的吡啶和吡啶羧酸衍生物制备某些卤代吡啶和卤代吡啶羧酸衍生物的方法。在该方法中,银阴极通过阳极化处理活化,阳极化处理包括将电势从0伏特的初始值增加至至少+0.3伏特和优选为+0.7伏特的最终值。但是,由于钝化,当进行转化时,反应速率通常降低,有时需要通过再次阳极化处理使阴极再活化以完成一次分批处理。期望得到活化阴极的改良方法,该方法对钝化更耐受并且允许较短的反应时间。
现在已经发现,通过在+1.0至+1.8伏特的最终电势活化阴极,反应速率变快,阴极不需要通常完成一次分批处理所需的再活化。更特别地,本发明涉及制备具有式I的3-卤代吡啶或3-卤代吡啶甲酸的改良方法
其中
X表示Cl或Br;
Y表示H、F、Cl、Br或C1-C4烷基,条件是当X是Cl时,Y不是Br;
R1表示Cl或CO2H;和
R2表示H或NH2
其中在相对于Ag/AgCl(3.0M Cl-)参比电极为-0.4至-1.7伏特的阴极电势,使直流或交流电流从阳极至银阴极通过具有式II的3,5-二卤代吡啶或3,5-二卤代吡啶羧酸的溶液,
其中
X、Y、R1和R2按之前定义,和
其中
两个X都为Cl或Br,
所述改良的特征在于在+1.0至+1.8伏特、优选为+1.2伏特的最终电势活化所述阴极。
该改良特别有利于从4-氨基-3,5,6-三氯吡啶-2-甲酸(毒莠定)制备4-氨基-3,6-二氯吡啶-2-甲酸(氯氨吡啶酸)。
本发明涉及用于3,5-二卤代吡啶或3,5-二卤代吡啶甲酸的5-卤代取代基的选择性电化学还原的改良方法。如本申请使用,术语“卤素”或“卤代”表示Cl或Br。碱金属表示锂、钠、钾、铷和铯,其中钠和钾是优选的。
还原例如4-氨基-3,5-二卤代吡啶甲酸中所包含的反应可以如下描述:
A)中和:
B)阴极反应:
C)阳极反应:
2(OH-)→1/2O2+H2O+2e-
D)总反应:
酸化反应混合物和通过常规技术回收产物来回收该羧酸。
所需电解还原通过本领域通常已知的技术进行。通常,使式II的起始物质溶解在溶剂中形成电解液,将该电解液添加到电解槽,同时足够的电流通过电解液直至达到所需程度的还原。
本领域技术人员应该知道,与相当的芳基氯化物电势相比,芳基溴化物的还原电势高0.5伏特(负的小一些)。溴总是首先还原掉。因此,当X是Cl时,Y不能是Br。
电解槽的设计是灵活的。电解可以按照间歇或按照连续或半连续的方式进行。电解槽可以是包含任何常规设计的电极或流动池的搅拌釜。在一些情况下,可以期望使用隔膜以将槽划分为阳极和阴极隔室。有用的隔膜材料的实例是各种阴离子和阳离子交换隔膜、多孔聚四氟乙烯、石棉、和玻璃。尽管使用三个电极是优选的,其中阴极的电势相对于参比电极进行控制,但是电解可以可替换地仅使用两个电极(阳极和阴极)和控制电解槽电流、电解槽电压、或同时控制两者来进行。为方便,优选3-电极未划分电解槽,其中电解液同时用作阴极电解液和阳极电解液。
阳极可以是任何化学惰性的材料,这包括例如铂、石墨、碳、金属氧化物例如银上的氧化银、或合金例如Hastelloy C,其中石墨、碳和Hastelloy C是优选的。阴极主要由银构成。电极的形式可以为板状、杆状、线材、筛、薄纱、毛织品、片材或槽,其中膨胀的网筛是优选的。阳极或阴极也可以由施涂于另一材料的涂层组成,其实例是涂布在钛上的贵金属氧化物例如氧化钌。
最优选的阴极是按照美国专利4,217,185和4,242,183中所描述制备的活化的银阴极。这样的活化的阴极可以通过使银微晶体的层沉积在导电基材上以形成复合电极或通过阳极化处理银电极本身制备。例如,为说明后者,未活化的银电极可以蘸入或浸入苛性物阴极电解液水溶液中并阳极化处理,由此将电极表面的一些银转化为氧化银并同时粗加工该表面。然后使电极的极性颠倒,使氧化物以电解方式转化为粘附于电极表面的微晶体银的颗粒。本发明改良的活化过程包括将电势从0伏特的初始值增加到至少+1.0伏特至+1.8伏特、最优选为+1.2伏特的最终值。氧化物沉积物的还原需要对阴极的负极化。将阴极电势从在氧化步骤过程中达到的+1.0至+1.8伏特的值逐渐降低到-0.5伏特或更低的值。在该方法中,不需要添加任何银到阴极电解液或碱的水溶液中。
通常,阴极在下述物质存在下活化:0.5至4wt%的碱金属氯化物、溴化物或硫酸盐,优选为NaCl;过量的碱金属氢氧化物,优选为1.0至4.0wt%NaOH;和另外存在的待还原的起始物质。便利地,起始物质存在的浓度与其在反应进料中的浓度相同,即,为1至20wt%,优选为8至12wt%。
水是用于电解的最优选的溶剂,但是在一些情况下,可以使用有机溶剂作为单独的溶剂或作为助溶剂。溶剂或助溶剂体系应该溶解全部或大部分起始物质和电解质,或至少足以使还原反应以合理的速率进行。而且,溶剂或助溶剂体系对于电解条件应该是惰性的,即,其不会改变阴极或阴极电解质物质或与阴极或阴极电解质物质反应达到无法接受的程度。除了水之外,优选的溶剂/助溶剂与水溶混并且包括较低分子量醇,醚例如四氢呋喃、二氧杂环乙烷和聚乙二醇醚,和低级酰胺如二甲基甲酰胺或二甲基乙酰胺。
需要碱金属氢氧化物用作支持电解质,NaOH和KOH是最优选的支持电解质。尽管NaCl是优选的盐,但是也可以使用其它盐,包括碱金属氯化物、溴化物、和硫酸盐。
在反应中,在3,5-二卤代吡啶甲酸的情况下,需要一当量的碱中和起始物质,需要另一当量碱产生在电解中消耗的氢氧根离子。该反应通常使用过量的碱进行,优选地在整个反应中使用1至4wt%过量的碱。
3,5-二卤代吡啶或3,5-二卤代吡啶甲酸在阴极电解质或进料中的浓度可以为1至20重量%,优选为8至12重量%。较低的浓度降低生产力,而较高的浓度通常导致收率较低、产物纯度较低和电效率较低。
电解的适宜温度通常为5至90℃。优选的温度范围是20至60℃。最优选的是30至50℃。
本领域技术人员会知道卤素选择性还原时的表观阴极电势取决于多种因素,包括,例如,特定基材的结构、槽构造、和分隔电极的距离。通常,相对于标准Ag/AgCl(3.0M C1-)电极的阴极电势对于Br应该为-0.4至-1.1伏特,对于Cl应该为-0.8至-1.7伏特。对于Br,阴极电势优选为-0.6至-0.9伏特。对于Cl,阴极电势优选为-1.0至-1.4伏特。以安培每平方厘米(amp/cm2)计的电流密度应该为至少0.005amp/cm2,优选为0.05amp/cm2或更高。
尽管产生分子氧是优选的,但是也可以使用很多其它阳极反应。实例包括产生分子氯或溴,氧化消耗物质例如甲酸盐或草酸盐以得到二氧化碳,或氧化有机物质以形成有价值的副产物。
在用于3,5-二卤代吡啶甲酸的操作的本发明优选模式中,将起始物质溶解在苛性碱盐水中以形成碱水溶液(例如,~10wt%卤化的4-氨基吡啶甲酸,~2.5wt%过量的NaOH和~1wt%NaCl),该溶液连续流通未划分的电化学槽,该槽具有在+1.2伏特在进料溶液的存在下通过阳极化处理活化的膨胀银网阴极。在使反应混合物保持碱性的同时,在相对于Ag/AgCl(3.0M C1-)参比电极为-0.6至-1.5伏特的阴极电势持续进行电解,直至达到所需程度的还原。所需产物通过常规技术回收。例如,通过酸化然后过滤或用不与水溶混的有机溶剂萃取,酸可以从反应混合物中沉淀。
以下实施例说明本发明。
实施例
制备4-氨基-3,5,6-三氯吡啶-2-甲酸(毒莠定)进料溶液
向4-升(L)烧瓶中添加2420克(g)热水、250g的50重量%NaOH、30g的NaCl、和300g毒莠定(95%)。将溶液搅拌30分钟(min),过滤通过1微米聚丙烯膜,并转移至5-L进料循环釜。该溶液重3000g并且包含9.5wt%的4-氨基-3,5,6-三氯吡啶-2-甲酸、2.0至2.5wt%的过量NaOH、和1.0wt%的NaCl。该进料溶液同时用于对比例和本申请的改良实施例。
实施例A通过在+0.7伏特阳极化处理制备4-氨基-3,6-二氯吡啶-2-甲酸(对比例)
向未划分的电化学槽中添加500g的毒莠定进料溶液。该进料溶液以4升每分钟(L/min)的速率和在43-45℃的温度流动通过一个未划分的电化学槽。银网电极的大小为1.8cm x 15.4cm。在+0.7伏特(V)进行正常阳极化处理之后,将槽的极性颠倒,并开始电解。阴极工作电势控制在相对于Ag/AgCl(3.0M C1-)参比电极为-1.35V。当进料循环时,在第一个5小时内添加总共10mL的50重量%NaOH以保持NaOH浓度为1.5-3.0%过量。电流开始为5.0amps并在24小时缓慢降至0.6amp。
在电解开始之后,不再需要阳极化处理。在8小时,槽流出物包含68%氯氨吡啶酸和26%毒莠定(都以HPLC面积%计)。在24小时,槽流出物包含88%氯氨吡啶酸和3.2%毒莠定。
实施例1通过在+1.2伏特阳极化处理制备4-氨基-3,6-二氯吡啶-2-甲酸
向实施例A中相同的未划分电化学槽中添加500g的毒莠定进料溶液。该进料溶液以4L/min的速率和在43-45℃的温度流动通过一个未划分的电化学槽。在+1.2伏特(V)进行正常阳极化处理之后,将槽的极性颠倒,并开始电解。阴极工作电势控制在相对于Ag/AgCl(3.0M C1-)参比电极为-1.35V。当进料循环时,在第一个5小时内添加总共10mL的50重量%NaOH以保持NaOH浓度为1.5-3.0%过量。电流开始为6.5amps并在24小时缓慢降至0.7amp。
在电解开始之后,不再需要阳极化处理。在8小时,槽流出物包含76%氯氨吡啶酸和17%毒莠定(都以HPLC面积%计)。在24小时,槽流出物包含88%氯氨吡啶酸和1.2%毒莠定。
Claims (2)
1.用于制备具有式I的3-卤代吡啶或3-卤代吡啶甲酸的改良方法
其中
X表示Cl或Br;
Y表示H、F、Cl、Br或C1-C4烷基,条件是当X是Cl时,Y不是Br;
R1表示Cl或CO2H;和
R2表示H或NH2
其中在相对于Ag/AgCl(3.0M Cl-)参比电极为-0.4至-1.7伏特的阴极电势,使直流或交流电流从阳极至银阴极通过具有式II的3,5-二卤代吡啶或3,5-二卤代吡啶甲酸的溶液,
其中
X、Y、R1和R2按之前定义,和
其中
两个X都为Cl或Br,
所述改良的特征在于所述银阴极通过在+1.2伏特的电势阳极化处理然后反向极化而活化。
2.权利要求1的方法,其中具有式I的3-卤代吡啶甲酸是氯氨吡啶酸,具有式II的3,5-二卤代吡啶羧酸是毒莠定。
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CN104198642B (zh) * | 2014-09-18 | 2015-11-25 | 中华人民共和国南通出入境检验检疫局 | 一种大麦中氯氨吡啶酸农药残留的检测方法 |
CN105803481B (zh) * | 2016-03-22 | 2018-03-27 | 浙江埃森化学有限公司 | 一种催化电解制备4‑氨基‑3,6‑二氯吡啶‑2‑甲酸的方法 |
CN110656345B (zh) * | 2019-08-23 | 2021-06-08 | 浙江工业大学 | 一种4-氨基-3,6-二氯吡啶甲酸的电解合成方法 |
CN113463115A (zh) * | 2021-07-01 | 2021-10-01 | 安徽工业大学 | Amp作为电解液电化学还原二氧化碳的应用 |
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EP2494095B1 (en) | 2009-10-27 | 2014-04-23 | Dow AgroSciences LLC | Improved silver cathode activation |
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US4242183A (en) * | 1979-04-13 | 1980-12-30 | The Dow Chemical Company | Highly active silver cathode, preparation of same and use to make 2,3,5-trichloropyridine |
US4217185A (en) * | 1979-07-02 | 1980-08-12 | The Dow Chemical Company | Electrolytic production of certain trichloropicolinic acids and/or 3,6-dichloropicolinic acid |
CN1394241A (zh) * | 2000-01-14 | 2003-01-29 | 美国陶氏益农公司 | 卤代的4-氨基吡啶甲酸的选择性电化学还原 |
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CN101235515A (zh) * | 2008-02-27 | 2008-08-06 | 浙江工业大学 | 一种活性银电极的制备方法 |
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US20130256148A1 (en) | 2013-10-03 |
US20110094893A1 (en) | 2011-04-28 |
CN102597328A (zh) | 2012-07-18 |
EP2494095A1 (en) | 2012-09-05 |
WO2011053582A1 (en) | 2011-05-05 |
US9090977B2 (en) | 2015-07-28 |
JP6200925B2 (ja) | 2017-09-20 |
KR101847795B1 (ko) | 2018-04-10 |
JP2016035108A (ja) | 2016-03-17 |
JP5818803B2 (ja) | 2015-11-18 |
EP2494095B1 (en) | 2014-04-23 |
KR20120089692A (ko) | 2012-08-13 |
KR101790803B1 (ko) | 2017-10-26 |
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US8685222B2 (en) | 2014-04-01 |
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