Química Orgânica I 2008/09 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 1 alkynes w3.ualg.pt\~abrigas QOI 0809 ALKYNE 2 1
Name these: 3 propyne 3 2 2 Br 5-bromo-2-pentyne 5-bromopent-2-yne 3 3 3 2 3 2,6-dimethyl-3-heptyne 2,6-dimethylpept-3-yne w3.ualg.pt\~abrigas QOI 0809 ALKYNE 3 Examples 3 2 2 4-methyl-1-hexen-5-yne 4-methylhex-1-en-5-yne O 3 2 3 4-hexyn-2-ol hex-4-yn-2-ol w3.ualg.pt\~abrigas QOI 0809 ALKYNE 4 2
ommon Names Named as substituted acetylene. 3 methylacetylene (terminal alkyne) 3 3 3 2 3 isobutylisopropylacetylene (internal alkyne) w3.ualg.pt\~abrigas QOI 0809 ALKYNE 5 Physical Properties Nonpolar, insoluble in water. Soluble in most organic solvents. Boiling points similar to alkane of same size. Less dense than water. Up to 4 carbons, gas at room temperature. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 6 3
Acetylene 1836 - Edmund Davy "a new carburet of hydrogen." An application of the discovery of acetylene gas by British chemist Edmund Davy in 1836 through the chemical reaction of calcium carbide with water. Acetylene produces light... http://www.latalaia.net/eng/aparador.asp?art=585&mail=1 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 7 Acetylene Marcellin Berthelot 1860 - acetylene Gustaf Dalén w3.ualg.pt\~abrigas QOI 0809 ALKYNE 8 4
welding torches. Acetylene In pure oxygen reaches 2800. Explodes to decompose to its elements w3.ualg.pt\~abrigas QOI 0809 ALKYNE 9 Synthesis of Acetylene eat coke with lime in an electric furnace to form calcium carbide. Then drip water on the calcium carbide. 3 + ao a 2 + coke lime O * a 2 + 2 2 O + a(o) 2 *This reaction was used to produce light for miners lamps and for the stage. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 10 5
Electronic Structure The sigma bond is sp-sp overlap. The two pi bonds are unhybridized p overlaps at 90 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 11 Bond Lengths More s character, so shorter length. Three bonding overlaps, so shorter. Bond angle is 180, so linear geometry. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 12 6
acetylide Acetylene acetylide N 2-, not by O - or RO -. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 13 Acidity Table w3.ualg.pt\~abrigas QOI 0809 ALKYNE 14 7
Forming Acetylide Ions + can be removed from a terminal alkyne by sodium amide, NaN 2. NaN 2 is produced by the reaction of ammonia with sodium metal. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 15 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 16 8
Alkynes from Acetylides Acetylide ions are good nucleophiles. S N 2 reaction with 1 alkyl halides lengthens the alkyne chain. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 17 Acetylide as base Acetylide ions can also remove + If back-side approach is hindered, elimination reaction happens via E2. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 18 9
Addition to arbonyl Acetylide ion + carbonyl group yields an alkynol (alcohol on carbon adjacent to triple bond). R + O R O 2 O + R O O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 19 Add to Formaldehyde Product is a primary alcohol with one more carbon than the acetylide. 3 + O 3 O 2 O + 3 O O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 20 10
Add to Aldehyde Product is a secondary alcohol, one R group from the acetylide ion, the other R group from the aldehyde. 3 3 3 + O 3 O 2 O + 3 3 O O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 21 Add to Ketone Product is a tertiary alcohol. 3 3 3 + O 3 O 3 3 3 2 O + O 3 O 3 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 22 11
Synthesis of alkynes Br Br 3 2 3 KO (fused) 200 3 2 3 Molten KO or alcoholic KO at 200 favors an internal alkyne. Sodium amide, NaN 2, at 150, followed by water, favors a terminal alkyne. 3 2 2 l 2 1) NaN 2, 150 3 2 2) 2 O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 23 double dehydrohalogenation Br Br R R KO ethanol R Br R NaN 2 R R Br Br R R NaN 2 R R w3.ualg.pt\~abrigas QOI 0809 ALKYNE 24 12
alkynes reactions w3.ualg.pt\~abrigas QOI 0809 ALKYNE 25 Migration of Triple Bond w3.ualg.pt\~abrigas QOI 0809 ALKYNE 26 13
Addition Reactions Similar to addition to alkenes. Pi bond becomes two sigma bonds. Usually exothermic. One or two molecules may add. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 27 Addition of ydrogen reduce alkyne to alkane Lindlar s catalyst, alkyne to a cis-alkene. sodium in liquid ammonia alkyne to a trans-alkene. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 28 14
Lindlar s atalyst Powdered BaSO 4 coated with Pd, poisoned with quinoline. 2 adds syn, so cis-alkene is formed. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 29 Na in Liquid Ammonia Use dry ice to keep ammonia liquid. As sodium metal dissolves in the ammonia, it loses an electron. The electron is solvated by the ammonia, creating a deep blue solution. N 3 + Na + Na + N 3 e - http://www.cci.ethz.ch/experiments/na-n3fl/en/stat.html w3.ualg.pt\~abrigas QOI 0809 ALKYNE 30 15
Mechanism Step 1: An electron adds to the alkyne, forming a radical anion Step 2: The radical anion is protonated to give a radical Step 3: An electron adds to the alkyne, forming an anion Step 4: Protonation of the anion gives an alkene w3.ualg.pt\~abrigas QOI 0809 ALKYNE 31 Addition of alogens l 2 and Br 2 add to alkynes to form vinyl dihalides. May add syn or anti, so product is mixture of cis and trans isomers. Difficult to stop the reaction at dihalide. 3 3 Br 2 3 Br Br 3 + 3 Br 3 Br 3 3 Br Br w3.ualg.pt\~abrigas QOI 0809 ALKYNE 32 Br 2 Br Br 16
Addition of X l, Br, and I add to alkynes to form vinyl halides. For terminal alkynes, Markovnikov product is formed. If two moles of X is added, product is a geminal dihalide. Br Br 3 3 2 Br 3 3 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 33 Br Br Br with Peroxides Anti-Markovnikov product is formed with a terminal alkyne. 3 Br Br 3 ROOR Br ROOR mixture of E and Z isomers Br 3 Br w3.ualg.pt\~abrigas QOI 0809 ALKYNE 34 17
ydration of Alkynes Mercuric sulfate in aqueous sulfuric acid adds -O to one pi bond with a Markovnikov orientation, forming a vinyl alcohol (enol) that rearranges to a ketone. ydroboration-oxidation adds -O with an anti-markovnikov orientation, and rearranges to an aldehyde. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 35 Mechanism for Mercuration Mercuric ion (g 2+ ) is electrophile. Vinyl carbocation forms on most-sub.. Water is the nucleophile. g + g +2 3 3 + 3 O an enol 3 O + 3 2 O g + O g + 3 O + w3.ualg.pt\~abrigas QOI 0809 ALKYNE 36 2 O 18
Enol to Keto (in Acid) Add + to the = double bond. Remove + from O of the enol. 3 O 3 O + 3 O 3 O A methyl ketone 3 O 2 O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 37 ydroboration Reagent Di(secondary isoamyl)borane, called disiamylborane. Bulky, branched reagent adds to the least hindered carbon. Only one mole can add. 3 3 3 B 3 3 3 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 38 19
ydroboration - Oxidation B and add across the triple bond. Oxidation with basic 2 O 2 gives the enol. 3 Sia 2 B 3 BSia 2 2 O 2 NaO 3 O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 39 Enol to Keto (in Base) + is removed from O of the enol. Then water gives + to the adjacent carbon. 3 O O 3 O 3 O An aldehyde 3 O O w3.ualg.pt\~abrigas QOI 0809 ALKYNE 40 20
Oxidation of Alkynes Similar to oxidation of alkenes. Dilute, neutral solution of KMnO 4 oxidizes alkynes to a diketone. Warm, basic KMnO 4 cleaves the triple bond. Ozonolysis, followed by hydrolysis, cleaves the triple bond. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 41 Reaction with KMnO 4 Mild conditions, dilute, neutral 3 2 3 KMnO 4 2 O, neutral O 3 arsher conditions, warm, basic O 2 3 O O KMnO 4, KO 3 2 3 3 O + O 2 3 2 O, warm w3.ualg.pt\~abrigas QOI 0809 ALKYNE 42 21
Ozonolysis Ozonolysis of alkynes produces carboxylic acids (alkenes gave aldehydes and ketones). O (1) O 3 3 2 3 3 O + (2) 2 O Used to find location of triple bond in an unknown compound. O O 2 3 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 43 w3.ualg.pt\~abrigas QOI 0809 ALKYNE 44 22
-M Organometalic ompounds RMgX An organomagnesium compound (a Grignard reagent) R 2 uli A lithium diorganocopper compound (a Gilman reagent) RLi An organolithium compound w3.ualg.pt\~abrigas QOI 0809 ALKYNE 45 3Li methyl lithium Nomenclature 3MgBr methyl magnesium bromide w3.ualg.pt\~abrigas QOI 0809 ALKYNE 46 23
Organometalic mpds arbon-metal bonds are polar covalent -M Bond -Li -Mg -Zn -u -g Difference in Electronegativity 2.5-1.0 = 1.5 2.5-1.2 = 1.3 Percent Ionic character* 60 52 2.5-1.6 = 0.9 36 2.5-1.9 = 0.6 24 2.5-1.9 = 0.6 24 *Percent ionic character = E - E M x 100 E w3.ualg.pt\~abrigas QOI 0809 ALKYNE 47.... solvents 3 2 O 2 3.... O Ethers work especially well since they can make complexes with Grignard reagents and solvate them. 3 2 2 2 3 O.... O.... 3.. O.. Mg.. O.. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 48 Br 24
Grignard Reagents basic and nucleophilic highly polar -Mg bond MgX http://www.nndb.com/people/260/000099960/ w3.ualg.pt\~abrigas QOI 0809 ALKYNE 49 Grignard reagents Grignard reagents are formed by reaction of an alkyl halide with magnesium metal in diethyl ether or tetrahydrofuran (TF) 3 2 2 2 l 1-hlorobutane + Mg ether 3 2 2 2 Mgl Butylmagnesium chloride w3.ualg.pt\~abrigas QOI 0809 ALKYNE 50 25
Grignard Reagents w3.ualg.pt\~abrigas QOI 0809 ALKYNE 51 Organolithium reagents Organolithium reagents are formed by reaction of an alkyl halide with lithium metal in a hydrocarbon solvent such as pentane 3 2 2 2 l + 2 Li pentane 1-hlorobutane 3 2 2 2 Li + Lil Butyllithium w3.ualg.pt\~abrigas QOI 0809 ALKYNE 52 26
2 3 2 2 2 Li + ui Butyllithium Gilman Reagents Prepared from an organolithium reagent and copper(i) iodide opper(i) iodide diethyl ether or TF ( 3 2 2 2 ) 2 u - Li + Lithium dibutylcopper (a Gilman reagent) + LiI w3.ualg.pt\~abrigas QOI 0809 ALKYNE 53 Gilman Reagents Gilman reagents can be used to form new carbon-carbon bonds by cross-coupling with alkyl or vinylic halides ( 3 ) 2 uli + 3 ( 2 ) 8 2 I ether or TF 3 ( 2 ) 8 2 3 + LiI + 3 u w3.ualg.pt\~abrigas QOI 0809 ALKYNE 54 27
Organozinc Reagents much less reactive than either RLi or RMgX to aldehydes and ketones. Simmons-Smith reaction w3.ualg.pt\~abrigas QOI 0809 ALKYNE 55 Acetylenic Reagents w3.ualg.pt\~abrigas QOI 0809 ALKYNE 56 28
Organometallics as bases Organometallics are strong bases and react with any proton donor stronger than the alkane from which they are derived δ- δ+ 3 2 -MgBr + -O pk a 15.7 Stronger acid 3 2 - pk a 51 Weaker acid + Mg(O)Br w3.ualg.pt\~abrigas QOI 0809 ALKYNE 57 3 : Any -O-, -S-, or -N- bonds are sufficiently acidic to react. O - - + O R 4 + ROO.. 3 :- + O 4 + :O.. -.. - - 3 : + O R 4 + :O.. R The reaction with 2 O also means that you must rigorously exclude water ( and water vapor = air ) from your reactions. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 58 29
Deuterated compounds ether 3 Br + Li 3 Li.. 3 : + D OD 3 D :O D Li + + Li +.. - - Br Li D ether Li D 2 O phenyllithium This reaction of an alkyllithium compound with water is generally not useful unless you use D 2 O, which is a way of placing a deuterium atom in your compound. w3.ualg.pt\~abrigas QOI 0809 ALKYNE 59 Organometalic oupling 2Li 3 2 2 2 Br pentane 3 2 2 2 Li + LiBr 3 2 2 2 Li + ui 3 2 h 2 h 2 2 u - Li + I 3 + ( 3 ) 2 uli + LiI + 3 u w3.ualg.pt\~abrigas QOI 0809 ALKYNE 60 30
Adaptado de: Organic hemistry, 6th Edition; L. G. Wade, Jr. Organic hemistry, 6 th edition; McMurry s http://dmdl.uvm.edu/chem/6_ch141.html http://www.cem.msu.edu/~reusch/virtualtext/addyne1.htm http://www.chem.uic.edu/web1/ool-ii/win/alkene/f4.tm http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/ carey04oc/ref/ch14organometalliccompounds.html#nomenclature w3.ualg.pt\~abrigas QOI 0809 ALKYNE 61 31