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The water–NaOH–agar gels of different compositions were studied and a ternary phase diagram wasprepared (Fig. 1). The following types of gels were obtained: (1) heterogeneous solution with solid phase containing agar (phase A), (2) heterogeneous solution with solid phase containing agar and alkali (phase B), (3) viscous liquid (phase C), (4) jelly-like highly vis-cous gel (phase D), (5) hard solid gel (phase E) or (6) heterogeneous solution with solid phase containing al-kali(phase F). Some compositions were non-gelling and merely gave either a simple solid–liquid mixtures with a large quantity of water (phase B) or solid–liquid mixtures with a very low quantity of water (phase A). Phase F denotes the compositions in which the base itself was not soluble in the corresponding quantity of water. A gel having 80–50% water: 4–24% sodium hydroxide: 16–34% agar agar could give a hard solid gel useful as the GEBC. We selected a GEBC having 60% water, 10% NaOH and 30% agar agar for the re-actions. It was a translucent dark brown solid (10% NaOH-GEBC). The GEBC pieces were about 2 mm thick and of irregular sizes of approximately 3–4 mm.The cyanoethylation of methanol with acrylonitrile was selected as a probe reaction to find out the opti-mum quantity of the GEBC required (Fig. 2). It was found that for 10 mmol of acrylonitrile 0.1 g of GEBC gave 100% yield of 3-methoxypropionitrile in 45 min. The quantity of GEBC corresponds to the 2.5 mole.% of NaOH with respect to acrylonitrile. When the reaction was carried out using the GEBC pieces of dif-ferent dimensions, the yield of the reaction was found to be constant within the limit of experimental error.It is interesting to observe that the cyanoethylation of 1-propanol is not reported by the classical procedure. For the cyanoethylation of 2-propanol a procedure is reported which uses solid KOH as a catalyst;[1] using this catalyst we obtained 80% of the prod-uct from 1-propanol. On the other hand, cyanoethylation of 1-propanol can be smoothly carried out using 10% NaOH-GEBC at 50◦C to obtain 96% of the product. Cellosolve, with benzyl alcohol could also be cyanoethylated effectively by the NaOH-GEBC (Table 1 ).For classical reactions, different catalysts have been reported [2]. 2-Methylpropan-2-ol and propan-2-ol could not be cyanoethylated and hence were used as solvents for the reaction. The cyanoethylation of other alcohols was then studied in the presence of 10% NaOH-GEBC. Also, except for methanol which caused slight whiten-ing of an otherwise dark brown coloured GEBC, noother alcohol seemed to have any effect on the GEBC nature. Apart from 1-propanol, 2-methyl-1-propanol was also cyanoethylated, this is not reported in the literature. To study the diffusion of alkali into a solvent, NaOH-GEBC was stirred in a few solvents and the amount of alkali diffusing into the solvents wasmonitored (Table 2). In 2-methylpropan-2-ol, ace-tone, toluene, and dichloroethane, the diffusion ofNaOH was practically zero; however, in alcohols with increasing polarity, the diffusion increased in he order 2-propanol < ethanol < methanol. The diffusion of NaOH into ethanol medium was also studied at three different temperatures (0, 28 and78◦C); the results showed that the diffusion was temperature-independent. In a blank experiment, the GEBC pieces were stirred in alcohol for the same time as the reaction duration and the same pieces were recycled in the subsequent blank reactions. The amount of NaOH in ethanol was determined after each reaction. Thus, in five successive cycles, the amount of NaOH that diffused from the GEBC was found to be 22, 7, 2, 0.6 and 0.6% of the amount of NaOH remaining after each cycle. Thus, we may say that deactivation of the catalyst is possible but depends to a certain extent on the solvent (maximum in the case of methanol). We may also say that it goes on decreasing in each successive cycle. |
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jiangguofeng
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shuoli: 金币+100, 翻译EPI+1, ★★★很有帮助, THANKS FOR HELP 2013-05-28 15:39:09
shuoli: 金币+100, 翻译EPI+1, ★★★很有帮助, THANKS FOR HELP 2013-05-28 15:39:09
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FOR REFERENCE ONLY 研究了不同的配方的水-NaOH-琼脂凝胶并作出三元相图（图1）。 得到下列各种凝胶：(1) 带有含琼脂固相的不均质溶液（A型）, (2) 带有含琼脂固相的不均质溶液（B型）, (3)粘性液体（C型）,(4) 胶冻状的高粘胶（D型），（５）硬固体凝胶（E型）或（６）带有含碱固相的不均质溶液（F型）。 某些配方是非凝胶的并且只能得到或者一种带有大量水的简单固体-液体混合物（B型）或者带有很低水量的固-液混合物（A型）。 F型表示其中的碱本身是不溶于相应量的水的配方。 含有80 - 50%水:４- 24%氢氧化钠的凝胶： 16 - 34%冻琼脂能得到一种作为GEBC使用的硬的固体凝胶。 我们选择含有60%水, 10% NaOH和30%冻琼脂的GEBC用于反应。 这是一种半透明的暗褐色固体（10% NaOH- GEBC）。 GEBC块大约２毫米厚，大约３-４毫米大小不一。 选择用丙烯腈对甲醇进行氰乙基化作为探针反应去查找需要的GEBC的最佳最佳存货数量（图２）。 结果发现10毫摩尔的丙烯腈、0.1克的GEBC于45分钟得到100%收率的３-甲氧基丙睛。 GEBC的用量与相对于丙烯腈2.5 摩尔%的NaOH相当。 当使用不同尺寸的GEBC块进行反应时,反应收率在实验误差范围内是不变的。 有趣的是注意到1-丙醇的氰乙基化没有被经典方法所报告。 2-丙醇的氰乙基化报导的方法是使用固体KOH作为催化剂; [1]使用这种催化剂由1-丙醇得到80%的产物。 另一方面，于50℃中，使用10% NaOH - GEBC，1-丙醇的氰乙基化能够顺利地进行并得到96%的产物。 溶纤剂与苯甲醇也可以用NaOH-GEBC进行氰乙基化（表1）。 使用不同催化剂的经典反应已经有过报导[２]。 叔丁醇和异丙醇不能被氰乙化，因此用作反应溶剂。然后研究了在10% NaOH - GEBC存在下其他醇类的氰乙基化。并且，除甲醇会引起别的方式着色的暗褐色GEBC轻微变白外,看来任何其他的醇类都不会对GEBC性质有影响。除1-丙醇以外,异丁醇也进行了氰乙基化,但这不是本文报告的内容。 为了研究碱加入一种溶剂中后的扩散作用，NaOH-GEBC于几种溶剂中搅拌，监测溶剂中扩散的碱的量（表２）。于叔丁醇、丙酮、甲苯和二氯乙烷中, NaOH的扩散作用几乎为零;然而于极性高的醇类中,扩散作用增大的顺序依次为2-丙醇<乙醇<甲醇。 NaOH于乙醇价质中的扩散作用也于三个不同温度（0，28和78℃）下进行了研究；结果显示扩散作用是与温度无关的。 于一个空白试验中, GEBC块于醇类中搅拌至反应结束，随后的空白反应中使用同样的GEBC块。每次反应后测定于乙醇中NaOH的量。这样于五个逐次循环中,观察到从GEBC中扩散的NaOH的量分别是每次循环后剩余NaOH量的22, 7, 2, 0.6和0.6%。因此我们可以说催化剂的惰性化是可能的，但是在某程度上是取决于溶剂的（在甲醇的情况下为最大）。我们也可以说于每次逐次循环中扩散的NaOH量在减少。 |
2楼2013-05-28 10:04:38