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Goals for the day: 1)Grignard Reaction 2)Ethers (Naming and reactions) 3)Epoxides (naming and reactions) 4)Thiols & sufides (reactions)

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Presentation on theme: "Goals for the day: 1)Grignard Reaction 2)Ethers (Naming and reactions) 3)Epoxides (naming and reactions) 4)Thiols & sufides (reactions)"— Presentation transcript:

1 Goals for the day: 1)Grignard Reaction 2)Ethers (Naming and reactions) 3)Epoxides (naming and reactions) 4)Thiols & sufides (reactions)

2 Alkyl, aryl, and vinylic halides react with magnesium in ether or tetrahydrofuran to generate Grignard reagents, RMgX Grignard reagents react with carbonyl compounds to yield alcohols 17.5 Alcohols from Carbonyl Compounds: Grignard Reagents

3 Grignard reagents act as nucleophilic carbon anions (carbanions = : R  ) in adding to a carbonyl group The intermediate alkoxide is then protonated to produce the alcohol Mechanism of the Addition of a Grignard Reagent

4 Try to predict the products…

5 Possible depictions are…

6 Try to fill in the mechanism…

7 Reactions of Grignard Reagents with Carbonyl Compound s

8 Yields tertiary alcohols in which two of the carbon substituents come from the Grignard reagent Grignard reagents do not add to carboxylic acids – they undergo an acid-base reaction, generating the hydrocarbon of the Grignard reagent Reactions of Esters and Grignard Reagents

9 Cannot be prepared if there are reactive functional groups in the same molecule, including proton donors Grignard Reagents and Other Functional Groups in the Same Molecule

10 Predict the product…

11 Remember it goes all the way to the alcohol & two CH3 groups are added…

12 Naming Ethers Ethers contain the R-O-R bond. Basically, you name the two groups attached to the oxygen (alphabetically) and add the term ether. The smallest ether is dimethyl ether

13 Ethers as attachments Methoxy Ethoxy isopropoxy

14 Pick one to try to name & panel submit

15 Isopropyl pheny ether Or Isopropoxy benzene Secbutyl vinyl ether Or 1-secbutoxy ethene

16 R–O–R ~ tetrahedral bond angle Oxygen is sp 3 -hybridized Oxygen atom gives ethers a slight dipole moment Not very reactive, so they make good solvents (diethyl ether is the “ether” we use in lab all the time). Not water soluble (although diethyl ether is slightly…see diagram on the following page)… Properties of Ethers

17 This is why you have to “dry” the organic layer in your reactions!

18 Diethyl ether prepared industrially by sulfuric acid– catalyzed dehydration of ethanol – also with other primary alcohols 18.2 Synthesis of Ethers

19 Works really only if the ether that you want is symmetric….otherwise you can get mixed results Synthesis of Ethers

20 Problem is.....propanol reacts with itself and ethanol reacts with itself… Need for an unsymmetric ether synthesis

21 Mechanism of ether formation from alcohols…

22 Reaction of metal alkoxides and primary alkyl halides and tosylates Best method for the preparation of unsymmetric ethers Alkoxides prepared by reaction of an alcohol with a strong base such as sodium hydride, NaH The Williamson Ether Synthesis

23 Predict the product...

24 The carbons of the alkyl halide become the “second” group of the ether...

25 An SN2 process… Note that the second step of the reaction is an SN2 process, so works best for primary alkyl halides (or methyl bromide)

26 Which is better? (you get phenyl propyl ether either way)…

27 Path “a” is better because the alkyl halide is primary and will react faster in the SN2 reaction

28 Cyclic ethers behave like acyclic ethers, except if ring is 3- membered Two common structures are ethylene oxide and THF Cyclic Ethers

29 Also called epoxides Epoxides (Oxiranes)

30 Treat an alkene with a peroxyacid Abbreviation for this reagent is MCPBA… Preparation of Epoxides Using a Peroxyacid

31 What’s the product?

32 Answer…

33 Addition of HO-X to an alkene gives a halohydrin Treatment of a halohydrin with base gives an epoxide Intramolecular Williamson ether synthesis Epoxides from Halohydrins

34 Water adds to epoxides with dilute acid at room temperature Product is a 1,2-diol (on adjacent C’s: vicinal) Mechanism: acid protonates oxygen and water adds to opposite side (trans addition) 18.6 Reactions of Epoxides: Ring-Opening

35 Anhydrous HF, HBr, HCl, or HI combines with an epoxide Gives trans product Halohydrins from Epoxides

36 Regiochemistry of Acid-Catalyzed Opening of Epoxides  1) Nucleophile preferably adds to less hindered site if primary and secondary C’s  2) Nucleophile adds to a tertiary carbon because of carbocation character 1) 2)

37 Steps of Acid-Catalyzed Opening of Epoxides 1)Protonation 2)Attack of the nucleophile from the backside Note: check for degree of substitution

38 Strain of the three-membered ring is relieved on ring- opening Hydroxide cleaves epoxides at elevated temperatures to give trans 1,2-diols Base-Catalyzed Epoxide Opening

39 Adds –CH 2 CH 2 OH to the Grignard reagent’s hydrocarbon chain Acyclic and other larger ring ethers do not react Addition of Grignards to Ethylene Oxide

40 Large rings consisting of repeating (-OCH 2 CH 2- ) or similar units Named as x-crown-y x is the total number of atoms in the ring y is the number of oxygen atoms 18-crown-6 ether: 18-membered ring containing 6 oxygen atoms Central cavity is electronegative and attracts cations 18.7 Crown Ethers

41 Thiols (RSH), are sulfur analogues of alcohols Named with the suffix -thiol SH group is called “mercapto group” (“capturer of mercury”) 18.8 Thiols and Sulfides

42 From alkyl halides by displacement with a sulfur nucleophile such as – SH The alkylthiol product can undergo further reaction with the alkyl halide to give a symmetrical sulfide, giving a poorer yield of the thiol Thiols: Formation and Reaction

43 Sulfides (RSR), are sulfur analogues of ethers Named by rules used for ethers, with sulfide in place of ether for simple compounds and alkylthio in place of alkoxy Sulfides

44 Reaction of an alkyl thiol (RSH) with bromine or iodine gives a disulfide (RSSR) The thiol is oxidized in the process and the halogen is reduced Cysteine amino acid forms cystine bonds Oxidation of Thiols to Disulfides

45 Thiolates (RS  ) are formed by the reaction of a thiol with a base Thiolates react with primary or secondary alkyl halide to give sulfides (RSR’) Thiolates are excellent nucleophiles and react with many electrophiles Sulfides

46 Have a wonderful day!

47 An ether has two organic groups (alkyl, aryl, or vinyl) bonded to the same oxygen atom, R–O–R Diethyl ether is used industrially as a solvent Tetrahydrofuran (THF) is a solvent that is a cyclic ether Thiols (R–S–H) and sulfides (R–S–R) are sulfur (for oxygen) analogues of alcohols and ethers Ethers and Their Relatives


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