22 Chap 11 : Ethers, Sulfides, and Epoxides 11.1 Structure of ethers 11.2 Nomenclature of ethers 11.3 Physical properties of ethers 11.4 Preparation o

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1 22 hap 11 : Ethers, Sulfides, and Epoxides 11.1 Structure of ethers 11.2 Nomenclature of ethers 11.3 Physical properties of ethers 11.4 Preparation of ethers 11.5 Reactions of ethers 11.6 lyl ethers as protecting groups 11.7 Epoxides: Structure and nomenclature 11.8 Synthesis of epoxides 11.9 Reactions of epoxides Ethylene oxide and epichlorohydrin: Building blocks in organic synthesis rown ethers Sulfides 11.1 Structure of Ethers Ether( 에테르혹은에터 ) : 두개의탄소원자사이에한개의산소원자가결합된 구조 o Dimethyl ether sp 3 - 에두쌍의비공유전자쌍이존재하며, -- 의결합각은두메틸기의반발력으로인하여정사면체의 o 보다약간증가한다. - 결합은극성을띄지만, 대칭성질로인하여 dipole moment 가상당히상쇄되므로약간의극성을띈다 Nomenclature of Ethers IUPA명 : 가장긴탄소사슬을모체 alkane으로선택하고, 치환된 -R기를 alkoxy( 알콕시 ) 로명명함. -기는 -R기보다우선권을가짐. 관용명 : 산소에결합된 alkyl+ether 분자량이작은 ether는주로관용명을사용함 Ethoxyethane (1R,2R)-2-Ethoxycyclohexanol 2-Methoxy-2-methylpropane (Diethyl ether) (trans-2-ethoxycyclohexanol) (tert-butyl methyl ether) 3

2 23 Polar protic solvent : Polar aprotic solvent : 2-Methoxyethanol (Methyl cellosolve) Dimethoxyethane(DME) 2-Ethoxyethanol (ellosolve) Diethylene glycol dimethyl ether(diglyme) yclic ether의명명포화고리에산소원자가존재하면접두사 ox-로나타내고, 3~6의고리는끝에각각 -irane, -etane, -olane, -ane를붙여준다. 고리원자의번호는산소원자로부터시작된다. xirane xetane xolane xane 1,4-Dioxane (Ethylene oxide) (Tetrahydrofuran) (Tetrahydropyran) 11.3 Physical Properties of Ethers 1) Ether 는산소원자에부분적인음전하와여기에결합된탄소원자에부분적인 양전하가발달되어극성분자이지만, 극성의세기는약하다. 2) 액체상태에서 ether 분자들사이에는약한 dipole-dipole interaction( 쌍극자 - 쌍극자상호작용 ) 이존재하므로 ether 는비슷한분자량을갖는 alcohol 의끓는 점보다훨씬낮다. Very weak dipoledipole interaction 3) Ether 는 hydrogen bond donor 로작용할수없기때문에 alcohol 보다물에훨 씬덜녹는다. 그러나 ether 는 hydrogen bond acceptor 로작용할수있기때 문에비슷한분자량의탄화수소보다물에더잘녹는다. hydrogen bonding

3 24 Table 11.1 : Boiling points and solubilities in water of some ethers and alcohols 문제 11.2 : rder of increasing boiling point 11.4 Preparation of Ethers A. Willamson Ether Synthesis 금속 alkoxide에의한 haloalkane의친핵성치환반응으로 ether의합성. Williamson ether 합성을계획할때친핵성치환이최대가되고, 경쟁적인 β-제거반응이최소가되도록반응물을조합하는것이필수적이다. 1 o, 2 o, 3 o alkoxide + 1 o haloalkane Na I 3 + NaI Sodium isopropoxide 2-Methoxypropane K I 3 + K potassium tert-butoxide 2-Methoxy-2-methylpropane + 3 Na Na tert-butyl bromide 2-Methylpropene 예제 11.3 : (a) + (b) 문제 11.3 :

4 25 B. Acid-atalyzed Dehydration of Alcohols 산촉매하에서 primary alcohol 을탈수 (- 2 ) 하면 ether 가생성된다 S 4 fast S st step : 2 S 4 에의한 -기의 protonation Poor leaving인 -기가 good leaving인 2 로전환됨 2nd step : 두번째 3 2 이 oxonium 중간체에 S N 2 치환반응을일으켜새로운 oxonium 중간체생성 3rd step : 2 가 oxonium 중간체의 + 를뽑아 diethyl ether의생성 산촉매하에서분자간탈수반응에의한 ether의합성은가지가없는 1차알코올로부터대칭 ether가생성될때수율 (yield) 이높다. 2차알코올로부터의 ether의생성은 β-elimination으로인한부반응이일어나며, 특히 3차알코올의경우는 alkene으로의탈수반응이주반응이다.. Acid-atalyzed Addition of Alcohols to Alkenes Preparation of tert-butyl methyl ether from 2-methyl-2-propene : tert-butyl methyl ether 3 1st step : 산촉매로부터 2-methyl-2-propene에 proton transfer( 양성자전이 ) 가일어나 3 o carbocation의생성 2nd step : 3 친핵체의첨가로옥소늄이온의생성 3rd step : Deprotonation( 탈양성자화 ) 이일어나 tert-butyl methyl ether의생성 Alkene에 alcohol의첨가에의한 ether의제조는안정한 carbocation을형성하고, methanol 혹은 1차 alcohol일때유용하다.

5 Reactions of Ethers Ether : Less reactive to chemical reaction K 2 r 2 7, KMn 4 와같은산화제와반응하지않으며, 강염기에서도안정 3차 alkyl ether를제외하고약한산에도영향을받지않음 Ether는반응에비활성이고, 좋은용매성질때문에유기반응의용매로널리사용됨 A. Acid-atalyzed leavage by oncentrated X Dialkyl ether는진한강산수용성 I(57%) 나 (48%) 과가열조건에서분해가일어나 alkyl iodide 혹은 alkyl bromide를생성한다. l(38%) 은 l - 가물속에서 - 또는 I - 보다친핵성이약하므로 dialkyl ether를분해시키기어렵다. + 2 heat Mechanism : + heat leavage of tertiary, allyl, benzyl ether by aq l + l + l l Tertiary, allyl, benzyl ether 는매우안정한 carbocation 을형성할수있으므로 온화한반응조건에서도수용성 l 에의한분해가용이하게일어난다. 예제 11.5 : + -I 예제 11.6 (b) : + -

6 27 B. Ether safety alert: Flammability and formation of hydroperoxides Et 2 나저분자량의 ether 사용시주의점 : i) Ether는끓는점이낮아휘발성이크고가연성물질이므로불꽃으로부터멀리하고환기 food를작동시켜놓고사용해야한다. ii) Ether는산소의옆에있는 -가 2 분자와 radical 반응하여폭발성을갖는 hydroperoxide( 하이드로과산화물 ) 를생성하므로오래된 ether를사용해서는안된다. 산소옆에있는 - 결합이 2차탄소인경우안정한 3차 radical 중간체를더빠르게생성하므로 hydroperoxide의생성속도는급속히증가한다. Diethyl ether ydroperoxide Diisopropyl ether ydroperoxide Ether 속에들어있는 hydroperoxide의검출및제거 : Ether를 10% KI 수용액으로처리할때노란색이관찰되면 hydroperoxide가존재하며, 황화철 (II) 의묽은황산수용액을넣어흔들어주면 hydroperoxide가제거된다 lyl Ethers as Protecting Groups Protecting group( 보호화기 ) : 두개이상의작용기를포함한유기화합물의반응에서한작용기의반응이잠시일어나지않도록해주는작용기. 보호화기는도입이용이해야하며, 보호화되지않은작용기를변환시키는동안반응이일어나지않아야하고, 원래작용기로재생하도록쉽게제거되어야한다. 1) Protecting group of alcohol 3 Et 3 l Et l l l 3 Et Trimethylsilyl chloride Triethylsilyl chloride tert-butyldimethylsilyl chloride Triisopropylsilyl chloride (TMSl) (TESl) (TBDMSl) (TIPSl) Reactivity : TMS-l > TES-l > TBDMS-l > TIPS-l Stability of silyl ether : R-TIPS > R-TBDMS > R-TES > R-TMS

7 28 lyl ether 는대부분의산화제나환원제에영향을받지않으며, 비수용성산이나 염기에안정하다. TBDMS 기는 p 2~12 범위내의수용액에안정하다. + l Et 3 N + Et 3 N + l TMS-l Trimethylsilyl ether 2) Deprotection of silyl ether Use of tetrabutylammoniun fluoride(bu 4 N + F - ) + Bu 4 N + F TF + F Tetrabutylammoniun fluoride(bu 4 N + F - ) 에의한 TBDMS-protected alcohol 의분 해는 -F σ 결합 (582 kj/mol) 이 - σ 결합 (368 kj/mol) 보다상당히강하기때 문에잘일어난다. 4-Pentyn-1-ol 로부터 4-heptyn-1-ol 의합성? 4-Pentyn-1-ol 4-eptyn-1-ol Synthetic scheme : + l Et 3 N 1) NaN 2 2) Bu 4 N + F + F

Oxidation of Alcohols 1 o Alcohol : RCH 2 OH [ O ] RCHO [ O ] RCOOH 2 o Alcohol : RR'CHOH [ O ] RCOR' 3 o Alcohol : R 3 COH [ O ] No oxidation

Oxidation of Alcohols 1 o Alcohol : RCH 2 OH [ O ] RCHO [ O ] RCOOH 2 o Alcohol : RR'CHOH [ O ] RCOR' 3 o Alcohol : R 3 COH [ O ] No oxidation 14 10.8 xidation of Alcohols 1 o Alcohol : RC 2 RC RC 2 o Alcohol : RR'C RCR' 3 o Alcohol : R 3 C o oxidation A. Chromic Acid 1) Formation of chromic acid Chromic acid는황산수용액에 chromium oxide( 3 ) 나 potassium