【烯烃的反应 Alkenes】

1、【烯烴的反應 Alkenes】(一)親電子加成反應Electrophilic Addition Reaction(A)原理Principle烯烴是不飽和烴。這種不飽和的性質除了可利用氫來補充外，還可以用其他試劑。此外，烯烴的不飽和使其擁有獨特的化學反應。因此，烯烴的典型反應為發生在 >C=C< 雙鍵上的加成反應。Alkenes are unsaturated hydrocarbons and as such can be changed into saturated compounds by the addition of hydrogen and other reagents.

2、This accounts for the characteristic chemical properties of a alkenes. Hence, the typical reactions of alkenes are addition reactions over the >C=C< double bond.由於烯烴的電子只是鬆散地連繫著，故它能夠作為電子源，並容易受到親電子體(缺電子類)或自由基的攻擊。在親電子加成反應中，試劑XY的X和Y分別加在烯烴的 >C=C< 雙鍵上。The loosely held -electrons in an alkene s

3、erve as a source of electrons. It invites the attack of an electrophile (electron deficient reagent) or a free radical.(B) 反應方程(C)反應機理親電子加成反應的一般機理如下所示：The general mechanism of electrophilic addition reaction is as follows:(二)烯烴之加成反應Addition Reactions of Alkenes(A)溴化氫的加成反應Addition of Hydrogen Bromide

4、a,反應Reaction在室溫下，溴化氫能迅速與烯烴反應，生成溴烷。這反應可藉著把乾燥的氣態溴化氫直接加進烯烴中來進行。須注意進行此反應時不宜採用溴化氫水溶液，這是避免水與烯烴進行加成反應。Hydrogen bromide reacts rapidly with alkenes at room temperature, yielding the bromoalkane. The reaction is carried out by passing dry gaseous hydrogenbromide directly into the alkene. Note that the aqueou

5、s solution of hydrogen bromide is not used in order to avoid addition of water to the alkene.親電子體溴烷b,反應機理Reaction mechanism含有C=C雙鍵的烯烴可成為多電子中心，並吸引缺電子的親電子體H-Br。此反應機理是由兩部分組成：The alkene, with its C=C double bond, acts as the electron rich centre. It attracts the electron-deficient electrophile, H-Br. Th

6、e mechanism consists of two parts:1.烯烴的加質子作用Protonation on the alkenes這是整個機理的速率控制步驟，並涉及不穩定的中間體碳陽離子的生成。This is the rate determining step of the whole mechanism and involves the formation of an unstable carbonium ion as their intermediate.Carbonium ion2.溴離子的攻擊Attacked by bromide ion碳陽離子是高度親電子的，故會被多電子的

7、溴離子所攻擊。The carbonium ion is highly electrophilic and is attacked by the electron-rich bromide ion.c,例子Examples以下是溴化氫的加成反應的一些例子。例1及2中的反應只會生成一種鹵烷，因為這些烯烴的雙鍵是對稱的。然而，例3中的反應卻可能會得到兩種生成物，這可透過反應機理來解釋。In examples 1 and 2, only one haloalkane is obtained because the double bond in the alkene is symmetrical. Ho

8、wever in example 3, it is possible to obtain two products, the reasons for which can be understood through the reaction mechanism.1.CH2=CH2 + HBr CH3CH2Br 2.CH3CH=CHCH3 + HBr CH3CHBrCH2CH33.Major ProductMinor Productd,注意Notes1.對稱烯烴symmetrical alkene須注意在對稱烯烴的加質子作用中，只會生成一種生成物。It should be noted that p

9、rotonation on a symmetrical alkene will produce only one final product.2.不對稱烯烴asymmetrical alkene在不對稱烯烴的加質子作用中，則會有兩種生成物產生。In an asymmetrical alkene, there are two possible positions for protonation to occur during the first stage of the reaction1-Propyl carbonium ion (1)2-Propyl carbonium ion (2)反應的

10、中間體是碳陽離子(或稱正碳離子)，即帶正電荷的碳原子。兩個碳陽離子的穩定性是不相同的。烷基可藉誘導效應把電子供給其相連並帶正電荷的碳陽離子。在這個情況下，該烷基便是施以正誘導(+I)效應(即推電子誘導效應)。2-丙基及1-丙基碳陽離子分別被兩個烷基及一個烷基所穩定。而與碳陽離子相連的烷基數目愈多，碳陽離子便愈穩定，且其生成速度亦愈快。因此，2-丙基碳陽離子是較穩定的，這亦可解釋最終生成物的相對產量。The reaction intermediate of the above reaction is the carbonium ion. The stability of the two carb

11、onium ions in the example above are different. By inductive effect, an alkyl group tends to donate electrons to the attached positively charged carbonium ion. The alkyl group is said to exert a positive inductive(+I) effect (i.e. electrondonating inductive effect). Since the l-propyl and 2-propyl ca

12、rbonium ions are stabilized by one alkyl and wo alkyl group(s) respectively: a greater number of alkyl groups bonded to carbonium ion stabilizes M on speeding up its formation. Thus, 2-propyl carbonium ion is comparatively more stable and this explains the relative yield of the final products.3.碳陽離子

13、的穩定性根據帶正電荷的碳原子上的烷基數量，可把碳陽離子分類為一級、二級及三級。而碳陽離子的穩定性乃跟隨下列趨勢。因此，在反應途徑中需要較低活化能的便是主生成物。The carbonium ion can be classified as primary, secondary or tertiary depending on the number of alkyl groups bonded directly to the positively charged carbon atom. It can be concluded that the stability of the haloalkan

14、e formed is directly related to that of the carbonium ion as shown below. So it gives the major reaction product that requires lower activation energy in the reaction pathway.須注意烷基的長度對它的推電子能力並無任何影響。例如以下這兩個一級碳陽離子所含的烷基有不同的長度，但它們擁有類似的穩定性。Notice that the length of the alkyl group has no effect on its el

15、ectron-donating power. For example, the following two carbonium ions: Both primary carbonium ions have similar stability even though the alkyl groups present in the two carbonium ions have different lengths.4.馬科尼科夫規則Markownikoffs rule馬科尼科夫規則指出：當分子HA加在一個不對稱的烯烴時，HA的氫原子會連結到合氫較多的不飽和碳原子上，而形成主生成物。when a m

16、olecule HA is added to an asymmetrical alkene, the major product is the one in which the hydrogen atom of HA attaches itself to the unsaturated carbon atom already carrying the larger number of hydrogen atoms.這碳原子與較多氫原子連結主生成物副生成物The carbon atom carrys the larger number of hydrogen atomsMajor product

17、Minor product(B)鹵的加成反應(鹵化作用)Addition of Halogen(Halogenation)a,反應Reaction在室溫室壓及無光的環境下，溴或氯的親電子加成反應會很易在有機溶劑(如CCl4)中發生；在有光的環境下，所發生的反應會是自由基加成反應。The electrophilic addition reaction of bromine or chlorine takes place readily in organic solvent (e.g. CCl4) at room condition and in the absence of light. In

18、the presence of light, free radical addition takes place instead.二鹵烷(無色)Dihaloalkane(colourless) b,例子：四氯甲烷中的鹵與烯烴的反應Example: the halogen in CCl4 ethane is decolourized by reacting with an alkene.在這反應中，紅棕色的溴會快速脫色。這提供了一個對不飽和化合物的有效測試。This reaction provides a useful test for unsaturation, as the reddish

19、brown bromine is rapidly decolourized.把一滴溶於CCl4的Br2加進烯烴中(左)，紅棕色的溴(中)會快速脫色(右)A drop of Br2 dissolved in CCl4 is added to an alkene. The reddishbrown Br2 is decolourized.(C)溴水(含HOBr)的加成反應Addition of Bromine water (Containing HOBr)當溴溶於水中時，便會建立下列平衡:When bromine dissolves in water, the following equilibr

20、ium is established.溴(I)酸Bromic(I) acid在溴(I)酸中，氧原子的負電性較溴原子的高，故它很容易與烯烴在室溫室壓下反應，生成溴醇，而溴水的紅棕色亦會脫色。The oxygen atom is more electronegative than the bromine atom in bromic(I) acid. It reacts readily with an alkene at room condition to form the halohydrin. The reddish brown bromine water is also decolouriz

21、ed in the reaction.連位溴醇Bromohydrin(D)濃硫酸的加成反應Addition of Concentrated Sulphuric Acida,硫酸氫烷酯Alkyl hydrogensulphate烯烴能與冷濃硫酸在0-15反應，生成硫酸氫烷酯ROSO3H。這種生成物會溶於酸層中，形成一無色溶液。Alkenes react with cold concentrated sulphuric acid at 0-15 to form alkyl hydrogensulphates, ROSO3H, which dissolve in the acid layer to

22、form colourless solutions.硫酸氫烷酯ColdAlkyl hydrogensulphateb,硫酸氫烷酯應用Applications alkyl hydrogensulphate硫酸氫烷酯的龐大基團(OSO3H)使其極不穩定，因而令硫酸氫烷酯可作兩方面的應用：The presence of the large bulky group(OSO3H) of the alkyl hydrogensulphate makes it very unstable. There are two applications of this reaction:1.分開烷烴與烯烴的混合物Se

23、paration of a mixture of alkanes and alkenes烯烴能被濃硫酸吸收但烷烴卻不能。因此，當水與有機相分開後，便可藉著加熱得回純烯烴。An alkene can be absorbed by concentrated sulphuric acid whereas an alkane cannot. After the separation of the aqueous and organic phases, the alkene can be regenerated on heating.Heat2.製備醇Production of alcohols若將硫酸

24、氫烷酯與水加熱，便會得到烷醇。在這個反應中，濃硫酸扮演著催化劑的角色。The alkyl hydrogensulphate(VI) reacts with water on heating to give an alcohol in which concentrated sulphuric acid acts as acatalyst.Heat(E)催化氫化作用Catalytic Hydrogenationa,烯烴氫化成烷Alkenes are hydrogenated to produce alkane 以體積細小的鉑、鈀及鎳作催化劑，並把烯烴與氫通過它們，便能把烯烴氫化成烷。Alkenes

25、 are hydrogenated by passing them together with hydrogen over a catalyst made up of finely divided platinum, palladium or nickel. An alkane is produced.烷Pt, Pd or Ni catalystHeat, pressureb,分析有機化合物Analyzing organic compounds這個反應有助於分析有機化合物：只要測定被一摩爾烯所吸收的氫摩爾數，便能推斷出分子中存在的雙鍵(或三鍵)的數目。The reaction is usefu

26、l in analyzing organic compounds. By measuring the number of moles of hydrogen that are absorbed by one mole of a hydrocarbon, the number of double(or triple) bonds present in its molecule can be deduced.CH2=CH2 + H2 CH3CH3c,人造牛油Margarine植物油(如棕櫚油)是由酯與帶雙鍵的長鏈羧酸混合而製得的。在室溫下，不飽和油擁有較低熔點，並以液態存在。而將這些油中的部分碳雙

27、鍵氫化，便能把液態油轉變為固體脂肪。故此，不飽和油的氫化作用在製造人造牛油的工業上十分重要。Vegetable oils, such as palm oil, are made up of esters with long chained carboxylic acids containing double bonds. Unsaturated oils usually have lower melting points and exist as liquids at room temperature. By hydrogenation of some of the carbon-carbon

28、 double bonds in these oils, liquid oils is converted into solid fats(margarine). Thus the hydrogenation of unsaturated oils is an important process in the margarine-making industry .(三)臭氧分解作用Ozonolysis(A)臭氧化物在低於20的溫度下，把臭氧通入四氯甲烷中的烯烴溶液內，便會生成臭氧化物。An ozonide is formed when ozone is bubbled through a so

29、lution of alkene in 1,1,1-trichloroethane at a temperature below 20.臭氧化物ozonide(B)臭氧化物水解成醛或酮把臭氧化物水解，可生成醛或酮。由於反應所生成的H2O2會進一步把醛氧化為烷酸，故需加入Zn/CH3COOH來幫助分解H2O2。The ozonide is then hydrolysed by adding zinc and ethanoic acid. Zn/CH3COOH added can help to decompose H2O2 formed in this reaction and prevents

30、 H2O2 from f urther oxidizing the aldehydes into alkanoic acid.醛或酮Aldehydes or ketones(C)臭氯分解作用用來分析C=C雙鍵的位置Analysing the position of the C=C double bond in the alkene molecule by ozonolysis這個反應牽涉C=C雙鍵中鍵與鍵的斷裂。只要分析臭氯分解作用的生成物，婦煜分子中C=C雙鍵的位置便可決定。The reaction is very useful in determining the structure of

31、 an alkene molecule as it involves the breakage of bothandbonds of C=C double bond. By analysing the products formed in ozonolysis , the position of the C=C double bond in the alkene molecule can be determined readily.(四)聚合作用Polymerization把稱為單體的簡單分子作大量結合，以組成聚合物，這過程便是聚合作用。把簡單的烯烴聚合便會生成一族長鏈加成聚合物。聚合作用主要

32、透過自由基連鎖反應來進行。Polymerization is the process of forming a polymer by joining together a large number of simple molecules, known as monomers. Simple alkenes polymerize to form a family of long chain addition polymers. The polymerization proceeds via free radical chain reaction.(A)反應機理:自由基加成反應Reaction m

33、achanism: free radical addition reaction這個反應的機理由三部分組成：鏈引發作用、鏈傳播作用及鏈終止作用。The reaction mechanism consists of three stages: chain initiation, chain propagation and chain termination.a,鏈引發作用Chain initiation過氧化物(如過氧化苯)是反應中的自由基引發劑。在發生鍵合均裂作用後，便會生成反應中的第一個自由基。A peroxide(e.g. benzoyl peroxide) is used as a fr

34、ee radical initiator. It undergoes homolytic bond fission to yield the first radical in the reaction. 過氧化苯Benzoyl peroxide過氧化苯所生成的自由基會與乙烯分子反應，生成另一自由基。The radical produced then reacts with the ethene molecule to form a new radical.b,鏈傳播作用Chain propagation自由基與另一乙烯分子反應，生成另一碳鏈較長的自由基。The new radical reac

35、ts with another ethene molecule to give another radical with a longer carbon chain.這過程經過多次重複後，便會建成一條長鏈的烷基自由基。在鏈傳播作用這個階段中，碳鏈會不斷增長而聚合物鏈亦開始形成。The process is then repeated many times, with the result that a long-chain alkyl radical is formed. In the chain propagation stage, the carbon chain is lengtheni

36、ng continuously, with a polymer chain being formed.c,鏈終止作用Chain termination在這階段中，自由基反應後生成一穩定的生成物分子(不再生成另一自由基)，而反應亦隨之結束。In the chain termination stage, radicals react to give a stable molecule and the reaction eventually stops.(B)加成聚合物Addition Polymera,聚乙烯Polyethene1.反應Reaction乙烯的自由基聚合作用是在200及高壓(約150

37、0 atm)下經由微量的過氧化物或氧引發物所引發。Free radical polymerization of ethene is brought about by traces of a peroxide or oxygen initiator at a temperature of 200 under very high pressure(about 1500atm). 其中n = 1000LDPEHDPE單體Monomer聚合物Polymer2.高、低密度聚乙烯High and low density polyethene聚乙烯是熱塑性塑膠，故在高溫時會軟化。根據不同的製造條件，可製出低

38、密度聚乙烯(LDPE)及高密度聚乙烯(HDPE)。低密度聚乙烯的分子質量介乎50000至3000000之間，高密度聚乙烯的分子質量可達3000000以上。Polyethene is a thermoplastic which will soften at a high temperature. Depending upon the manufacturing conditions, low density polyethene (LDPE) and high density polyethene (HDPE) can be made. Low density polyethene with a

39、 molecular mass between 50000 and 3000000. High density polyethene with a molecular mass up to 3000000. 3.應用Applications低密度聚乙烯具有彈性及低熔點，可用來製造一些較柔軟的物質，如洗滌瓶、膠袋、玩具、膠喉及食物保鮮紙。高密度聚乙烯性質一般較為堅韌及其有較高的熔點，這類塑膠可用來製造較堅硬的物件，如牛奶瓶、堅硬的瓶及壺、洗衣容器、玩具及水桶。LDPE are light, flexible and has a low melting point. It is used to m

40、ake soft items such as wash bottles, plastic bags, toys, pipes and food wraps. HDPE are tougher and has a higher melting point. It is used to make more rigid items such as milk bottles, tough bottles and jugs, toys, and water buckets.b,聚丙烯Polypropene1.反應Reaction聚丙烯的聚合可在約200及溫和的壓強下把丙烯通過磷酸催化劑而製得。Prope

41、ne is polymerized by passing it over a phosphoric(V) acid catalyst at about 200 and subjected to a moderate pressure.單體Monomer聚合物Polymer聚合物Polymer2.應用Applications根據丙烯內甲基的不同方位，聚丙烯可以不同的組態存在，故聚丙烯的性質可藉製造條件的改變而有所不同。聚丙烯可用來製造水管、地氈、電池外殼、倒模零件、纖維、活門、繩索、包裝紙及保護性盔甲。Polypropene can exist in different configuratio

42、ns depending upon the orientation of the methyl group in propene. Properties of polypropene can therefore be modified by adjusting the conditions of manufacture. Polypropene is used to make pipes, carpeting, battery cases, moulded auto pads, fibres, valves, ropes, wrapping films and artificial turf.c,聚苯乙烯Polyphenylethene(or Polystyrene)1.反應Reaction苯乙烯可在85-100下，以過氧化二苯作引發劑而聚合。Phenylethene(styrene) polymerizes