二甲基丙烯醛

We prepared the pyrethric acid II through four reactions: esterification, oxidation, decomposition, diesterification. And the original synthesis route of the pyrethric acidII was improved: the yield of oxidation of allyl rise through increasing the activity of Selenium dioxide; in the document, tert-butyl-trans -2, 2-dimethy1-3-(2"-methoxycarbony1-1"-propenyl)cyclopropanecarboxy late was synthesized from tert-butyl-trans-2,2-dimethyl-3-(2 -formyl-r -propenyl) cyclopropanecarboxylate with two steps, with low yield.

我们经过酯化，氧化，成双酯，热分解四步反应，成功地得到了第二菊酸，并改进了原第二菊酸的合成路线：通过改变二氧化硒的活性提高了烯丙甲基的氧化产率；将原路线中醛氧化成羧酸、羧酸酯化的两步反应改为醛和甲醇、二氧化锰等作用一步直接酯化的方法，减少了反应步骤，提高了总收率。

The results showed that there were 8 kinds of aliphatic, 5 kinds of esters, 2 kinds of aldehydes, 2 kinds of nitrogen sulfur heterocyclic rings and one kind of hydrocarbon, alcoholics, ketone, lactones respectively in the analyzed 21 kinds of aroma components, and the content of furfural,β-methyl valeric acid, palmitic acid, nicotine, neohytadiene were higher, next were acetyl ethyl propionate, caleric acid, phenyl ethyl acetate, hydroxylic diethyl succinate.

结果表明，在分析出的21种香气成分中，分别有脂肪酸类8种，酯类5种，醛类2种，氮硫杂环类2种，烃类、醇类、酮类、内酯类各l种，其中相对含量较高的物质成分是糠醛、β-甲基戊酸、十六碳酸、烟碱、新植二烯，其次是乙酰丙酸乙酯、异戊酸、苯乙酸乙酯、羟基丁二酸二乙酯等。

Now, however, all children continue in "comprehensive" schools, and the eleven-plus determines which courses of study the child will follow.

然而现在，所有的孩子都要在综合学校继续学习，所以这次考试只是决定他们将要学习哪些课程。

Cultivatable land , and led to a general recognition that development must not be carried at the cost of agriculture .

城区的迅速扩大在很多情况下侵占了宝贵的可耕地，使人们普遍认识到发展不能以牺牲农业为代价。