§13 羧 酸

1. §13 羧 酸 Carboxylic Acids

2. A great many of carboxylic acids are found in nature. For example, acetic acid is the chief organic component of vinegar; butanoic acid is responsible for the odor of sour butter; Hexanoic acid (capoic acid ) is responsible for the unmistakable aroma of goats and dirty gym socks.

3. Cholic acid is a major component of human bile. Cholic acid

4. Cholic acid

5. §13.1 羧酸的结构、命名和分类 1 结构： 125pm 152pm 119 131pm 119 122

6. 乙酸结构的物理参数：

7. 2 命名 构型+取代基+ 某酸 选含有羧基的最长碳链为母体，从羧基碳开始编号， 根据母体的碳原子数目称为某酸。 2.1 IUPAC IUPAC rules allow for two systems of nomenclature, depending on the complexity of the acid molecule. Carboxylic acids that are derived from openchain alkanes are systematically named by replaceing the terminal -e of the correspoding alkane name with –oic acid. The carboxyl carbon atom is numdered C1 in this system. （2E,4E）-2,4-己二烯酸 4-甲基戊酸

8. Alternatively, compounds that have a –COOH group Bonded to a ring are named using the –carbooxylic acid. The COOH carbon is attached to C1 and is not itself Numbered in this system. 3-溴环己基甲酸 1-环戊烯基甲酸

9. 练习：命名下列化合物。 顺-1,3-环己基二甲酸 2-苯基丙酸 1-（4-甲基环戊烯基）甲酸

10. 2 俗名（惯用名） Because many carboxylic acids were among the first organic compounds to be isolated and purified, a large number of common names are recognized by IUPAC, some of which are given below. 一元酸 系统命名 普通命名 HCOOH 甲酸 蚁酸 CH3COOH 乙酸 醋酸 CH3CH2COOH 丙酸 初油酸 CH3CH2CH2COOH 丁酸 酪酸 CH3(CH2)16COOH 十八酸 硬脂酸

11. 含有二个羧基的羧酸称为二元酸 二元酸 系统命名 普通命名 HOOCCOOH 乙二酸 草酸 HOOCCH2COOH 丙二酸 缩苹果酸 HOOC(CH2)2COOH 丁二酸 琥珀酸 (Z)-HOOCCH=CHCOOH 顺丁烯二酸 马来酸 (E)-HOOCCH=CHCOOH 反丁烯二酸 富马酸

12. 3 分类 3.1 根据烃基分类 R

13. 3.2 根据羧基数目分类 草酸 柠檬酸、枸橼酸 可用于泡腾剂、糖浆剂、口服液制剂PH值调整以及部分固体制剂中适当加入可改善其贮藏稳定性。

14. §13.2 羧酸的物理性质和光谱性质 1. 状态与水溶性 低级脂肪酸是液体，可溶于水(C4以下与水混容），具有刺鼻的气味; 中级脂肪酸也是液体，部分地溶于水，具有难闻的气味; 高级脂肪酸是蜡状固体。无味，在水中溶解度不大（溶解度随烃基 的增大而减少）。 2. 熔沸点 液态脂肪酸以二聚体形式存在。所以羧酸的沸点比分子质量相当的醇高。 甲酸和乙醇的相对分子质量皆为46，而沸点：甲酸为100.7 乙醇为78.3 Acetic acid dimer

15. 3. 羧酸的光谱特征 1HNMR R2CHCOOH H： 10~12 HCR2COOH H： 2~2.6 IR光谱 羧酸中的C=O： 单体 二缔合体 RCOOH 1770~1750cm-1 ~1710cm-1 CH2=CHCOOH ~ 1720 cm-1 ~1690cm-1 ArCOOH 1700-1690cm-1 羧酸中的OH：~ 3550 cm-1 3000 ~2500cm-1 羧酸中的C-O ~ 1250 cm-1 由于羧酸的缔合作用，其IR中的OH的伸缩振动吸收常表现为：强宽峰，其中心在 3000cm-1附近。

16. 缔合的OH 练习：根据下列谱图信息给出其结构。

17. 1H NMR spectrum (CDCl3, 500 MHz)

18. 13C NMR spectrum (CDCl3, 125 MHz)

19. positive EI Mass Spectrum

20. 结构分析

21. §13.3 羧酸的酸性 大于醇，小于无机酸 讨论：ⅰ ⅱ

22. 解释： Since a carboxylate ion is more stable than an alkoxide ion, it is lower in energy and more highly favored at eqilibrium, as shown in the reaction energy diagram below.

24. 实验事实1 ⅲ 影响酸性强弱的因素

25. 实验事实2

26. 实验事实3 酸性与吸电子基团的数目成正比。

27. 结论 （1）电子效应 取代羧酸的酸性与吸电子基团的吸电子能力、多少、距离成正比。 （2）空间效应： 利于H+离解的空间结构酸性强，不利于H+离解的空间结构酸性弱.

28. （3）分子内的氢键也能使羧酸的酸性增强。

29. ⅳ 取代芳香族羧酸的酸性 结论：羧基的对位连有吸电子基时，其酸性增强，反之，其酸性减弱。

30. ⅴ 取代基位置对酸性的影响 取代基具有吸电子共轭效应时，酸性强弱顺序为： 邻 > 对 > 间 取代基具有给电子共轭效应时，酸性强弱顺序为： 邻 > 间 > 对 解释： 邻 位（诱导、共轭、场、氢键效应、空间效应 均要考虑。） 对 位（诱导很小、共轭为主。） 间 位（诱导为主、共轭很小。）

31. 实 例 邻 位 间位 对位 诱导吸电子作用大、 共轭给电子作用大、 氢键效应吸电子作用大。 诱导吸电子作用小、 共轭给电子作用大。 诱导吸电子作用中、共轭给电子作用小。 pKa 2.98 pKa 4.07 pKa 4.48 苯甲酸的 pKa 4.19

32. 练习：排列下列化合物的酸性强弱顺序。

33. §13.4 酰化反应 定义：羧酸中OH被烃氧基、氨（胺）基、卤素、酰氧基 等基团取代的反应。 1 酯化反应-----形式上OH被烃氧基取代得到酯的反应。 酯化反应是一个可逆的反应，为了使正反应有利，通常采用的手段是： ①使原料之一过量。 ②不断移走产物（例如除水，乙酸乙酯、乙 酸、水可形成三元恒沸物 bp 70.4℃）。 *反应也可在分子内发生。机理将在下章讨论。

34. ③ Polyesters The most generally useful polyester is that made by reaction between dimethyl terephthalate ethylene glycol. The product is used under the trade name Dacron to make clothing fiber and tire cord, and under the name Mylar to make recording tape. The tensible strength of poly(ethylene Terephthalate) film is nearly equal to that of steel.

35. ④与重氮甲烷生成甲酯的反应 100%

36. 2 生成酰胺和腈的反应 讨论：ⅰ 酰胺在脱水剂五氧化二磷存在下，加热可将酰胺转变成腈； ⅱ 反应用伯胺或仲胺时，得到N-烃基酰胺； ⅲ 反应在分子内发生时，得到内酰胺； ⅳ 腈可转变成羧酸、酰胺、胺、醛和酮。，条件如下：

37. 腈的转变

38. 腈的碱性水解、还原成醛的机理（亚胺中间体）腈的碱性水解、还原成醛的机理（亚胺中间体） DIBAH

39. 练习：

40. ⅴ 应用实例：尼龙66的合成（Wallace Hume Carothes 发明） 270oC 1MPa nHO2C(CH2)4COOH + nH2N(CH2)6NH2 + nH2O Nylon66 Nylons are used both in engineering applications and in making fibers. A combination of high strength and abrasion resistance makes nylon an excellent metal substitute for bearings and gears. As fiber,nylon is used in a wide variety of applications, from clothing to tire cord to Perlon mountaineering ropes.

41. Wallace Hume Carothers(1896-1937) was born in Burlington, Iowa, and received his Ph.D. at the University of illinois in 1924 with Roger Adams. He began his career with brief teaching positions at the University of South Dakota , the universityof Illinois, and Harvard Universuty , but moved to the Du Pont Company in 1928 to head their new chemsitry research program in Polymers. A prolonged struggle with depression led him to suicide after only 9 years at Du Pont.

42. Wallace Hume Carothers (b. April 27, 1896, d. April 29, 1937) can be considered the father of the science of man-made polymers and the man responsible for the invention of nylon and neoprene. The man was a brilliant chemist, inventor and scholar and a troubled soul. Despite an amazing career, Wallace Carothers held more than fifty patents; the inventor ended his own life. Wallace Carothers was born in Iowa and first studied accounting and later studied science (while teaching accounting) at Tarkio College in Missouri. While still an undergraduate student, Wallace Carothers became the head of the chemistry department. Wallace Carothers was talented in chemistry but the real reason for the appointment was a personnel shortage due to the war effort (WWI). He received both a Master's degree and PhD from the University of Illinois and then became a professor at Harvard, where he started his research into chemical structures of polymers in 1924.

43. In 1928, the DuPont chemical company opened a research laboratory for the development of artificial materials, deciding that basic research was the way to go -- not a common path for a company to follow at the time. Wallace Carothers left Harvard to lead Dupont's research division. A basic lack of knowledge of polymer molecules existed when Wallace Carothers began his work there. Wallace Carothers and his team were the first to investigate the acetylene family of chemicals. In 1931, DuPont started to manufacture neoprene, a synthetic rubber created by Carothers' lab. The research team then turned their efforts towards a synthetic fiber that could replace silk. Japan was the United States' main source of silk, and trade relations between the two countries were breaking apart. By 1934, Wallace Carothers had made significant steps toward creating a synthetic silk by combining the chemicals amine, hexamethylene diamine and adipic acid to create a new fiber formed by the polymerizing process and known as a condensation reaction. In a condensation reaction, individual molecules join with water as a byproduct. Wallace Carothers refined the process (since the water produced by the reaction was dripping back into the mixture and weakening the fibers) by adjusting the equipment so that the water was distilled and removed from the process making for stronger fibers. DuPont patented the new fiber as "nylon" the following year.

44. Polymers are any of a class of natural or synthetic substances composed of very large molecules called macromolecules that are multiples of simpler chemical units called monomers. Polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, nucleic acids, natural rubber and silk. Those synthesized in the laboratory have led to such commercially important products as plastics, synthetic fibers and synthetic rubber. See also: Polymers a brief description Acetylene is a colorless gas and the simplest and best-known member of the hydrocarbon series (molecules containing one or more pairs of carbon atoms linked by triple bonds), called the acetylenic series or alkynes. Explosive on contact with air, it is stored dissolved under pressure in acetone and used to make neoprene rubber, plastics, and resins. In metal welding, the oxyacetylene torch mixes and burns oxygen and acetylene to produce a very hot flame (as high as 6300°F).

45. Nylon, a synthetic thermoplastic material introduced in 1938, is a strong elastic, resistant to abrasion and chemicals and low in moisture absorbency. Extract from "Fortune Magazine" about nylon circa 1938: "nylon breaks the basic elements like nitrogen and carbon out of coal, air and water to create a completely new molecular structure of its own. It flouts Solomon. It is an entirely new arrangement of matter under the sun, and the first completely new synthetic fiber made by man. In over four thousand years, textiles have seen only three basic developments aside from mechanical mass production: mercerized cotton, synthetic dyes and rayon. Nylon is a fourth."

46. In 1936, Wallace Carothers married Helen Sweetman, a fellow employee at DuPont. They had a daughter, but tragically Wallace Carothers committed suicide before the birth of this first child. It was likely that Wallace Carothers was a severe manic-depressive, and the untimely death of his sister in 1937 added to his depression. A fellow Dupont researcher, Julian Hill, had once observed Carothers carrying what turned out to be a ration of the poison cyanide. Hill remarked that Carothers could list all the famous chemists who had committed suicide. In April of 1937, Wallace Hume Carothers consumed that ration of poison himself and added his own name to that list. Nylon, the miracle fiber, was introduced to the world in 1938.

47. 3 生成酰卤的反应 * 亚硫酰氯也是常用的氯化剂，酰卤是常用的酰基化试剂、反应中间体。

48. 4 生成酐的反应 *酸酐也是常用的酰基化试剂及重要的反应中间体

49. §13.5羧酸的其它反应 1 脱羧 讨论：ⅰ 一般为自由基机理；当α-C上连有羰基等吸电子基团时， 经历了环状过度态或羧酸负离子中间体，很易脱羧； ⅱ脱羧反应在合成上用于碳链的降级（减少一个碳）， 可将羧酸转变成少一个碳的卤代烃及其它有机物。

50. 脱羧反应 反应名称 反 应 式 适用范围 电解 10C左右的羧酸 柯尔伯法 (Kolbe) 2CH3COONa C2H6 + CO2 + NaOH + H2 2H2O AgNO3 KOH 产率1oRX最好，2oRX之, 3oRX最低。 RCH2COOH RCH2COOAg 汉斯狄克法 (Hunsdicker)  Br2 CCl4 RCH2Br HgO RCH2COOH RCH2COOHg 克利斯脱法 (Cristol S) 产率1oRX最好 Br2 CCl4  RCH2Br Pb(OAc)4 I2 RCOOH RCOOPb(OAc)3 产率1o、2o、3oRX均很好。 柯齐法 (Kochi) LiCl C6H6  RCl Pb(OAc)4 I2 Cl4 光 RI 珀脱法 RCOOH