Aliphatic Ethers

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Aliphatic Ethers. Pharmacy Student. Ethers have two alkyl groups bonded to an oxygen atom. Ethers R-O-R or R-O-R ´ C n H 2n+2 O. Ethers R-O-R or R-O-R ´ C n H 2n+2 O. Nomenclature of Ethers. Simple ethers are usually assigned common names. To do so: - PowerPoint PPT Presentation

Text of Aliphatic Ethers

Slide 1

Aliphatic Ethers

Pharmacy StudentEthers have two alkyl groups bonded to an oxygen atom.

Ethers R-O-R or R-O-R CnH2n+2OEthers R-O-R or R-O-R CnH2n+2O

Simple ethers are usually assigned common names. To do so: Name both alkyl groups bonded to the oxygen, arrange these names alphabetically, and add the word ether.For symmetrical ethers, name the alkyl group and add the prefix di-.Nomenclature of Ethers

More complex ethers are named using the IUPAC system. One alkyl group is named as a hydrocarbon chain, and the other is named as part of a substituent bonded to that chain:Name the simpler alkyl group as an alkoxy substituent by changing the yl ending of the alkyl group to oxy.Name the remaining alkyl group as an alkane, with the alkoxy group as a substituent bonded to this chain.

The oxygen atom in alcohols, ethers and epoxides is sp3 hybridized. Alcohols and ethers have a bent shape like that in H2O.The bond angle around the O atom in an alcohol or ether is similar to the tetrahedral bond angle of 109.5.Because the O atom is much more electronegative than carbon or hydrogen, the CO and OH bonds are all polar

Hydrogen bonding make ROH more soluble and have higher b.p. than ROR or RH .

8Preparation of Alcohols, EthersAlcohols and ethers are both common products of nucleophilic substitution.

The preparation of ethers by the method shown in the last two equations is called the Williamson ether synthesis.Methods of Preparetion:1- Williansons continuous etherification

Primary alcohols can dehydrate to ethersThis reaction occurs at lower temperature than the competing dehydration to an alkene.

Step 1 CH3CH2-OH H+ CH3CH2-OH2 -H2O CH3CH2Step2 CH3CH2 + HO-CH2CH3 CH3CH2-O-CH2CH3 HStep 3CH3CH2-O-CH2CH3 H+ CH3CH2-O-CH2CH3 H HSO4- diethyl ether -Williamson continuous etherification1) The Williamson Ether Synthesis :

Reaction of an alkoxide with an alkyl halide or tosylate to give an ether.

Alkoxides are prepared by the reaction of analcohol with a strong base such as sodium hydride (NaH)

The Williamson ether synthesis is an SN2 reaction. Synthesis of Ethers

Weve Already Seen Ether Synthesis by Alcohol Dehydration: Utility of this Reaction is Limited in its Scope: Mixture of Ether/Alkenes with 2 Alkyl Groups

Exclusively Alkenes with 3 Alkyl Groups

Only Useful for Synthesis of Symmetric Ethers ROH + ROH ROR + ROR + RORWilliamsons Synthesis1- Reaction with alkali metal (Na- K)R OH + Na R ONa + H2RONa + RX ROR + NaX

C2H5ONa + CH3Cl C2H5 O CH3 Williamson Synthesis of EthersUnsymmetrical Ethers From RONa + Halide, Sulfonate, etc. Utility of this Reaction is Much Greater Than Condensation:

Works with 1 and 2 Halides, Sulfonates, etc.

Still Exclusively Alkenes with 3 Alkyl Groups

Lower Temperatures Favor Substitution over Elimination

SN2 Conditions Apply Prefer Unhindered Substrate

Chemical PropertiesEther linkage is quite stable towards bases, oxidizing and reeducing agents.

Cleavage takes place under quite vigorous conditions as conc. Acids.Reaction of Ethers with Strong AcidIn order for ethers to undergo substitution or elimination reactions, their poor leaving group must first be converted into a good leaving group by reaction with strong acids such as HBr and HI.

HBr and HI are strong acids that are also sources of good nucleophiles (Br and I respectively).

When ethers react with HBr or HI, both CO bonds are cleaved and two alkyl halides are formed as products.

The mechanism of ether cleavage is SN1 or SN2, depending on the identity of R.

When 2 or 3 alkyl groups are bonded to the ether oxygen, the CO bond is cleaved by an SN1 mechanism involving a carbocation. With methyl or 1 R groups, the CO bond is cleaved by an SN2 mechanism.The mechanism of ether cleavage is SN1 or SN2, depending on the identity of R.

When 2 or 3 alkyl groups are bonded to the ether oxygen, the CO bond is cleaved by an SN1 mechanism involving a carbocation. With methyl or 1 R groups, the CO bond is cleaved by an SN2 mechanism.

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1-Action of HIR-O-R HI/ Low tempROH + RIHI / High temp2RI + H2OCH3-O-CH3

CH3OH + CH3I2 CH3I + H2OThis reaction can proceed by :1- SN1 or SN2. .. H + H R-O-R R-O-R .. + I- SN2 RI + R-OH (R is 10 or 2o ) SN1 R+ + ROH

I- RI ( R 3o) Action of PCl5:R-O-R + PCl5 2R-Cl + POCl3C2H5-O-C2H5 + PCl5 2CH3CH2Cl + POCl3 Thiols (RSH) is sulfur analogs of alcohols and

ethers, respectively Sulfur replaces oxygen

Thio Alcohols (Mercptants) R-SH Thiols Thiols (RSH), also known as mercaptans, are sulfur analogs of alcohols

They are named with the suffix thiolSH group is called mercapto group (capturer of mercury)Thiols are prepared from alkyl halides by SN2 with NaSH

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

Methods of preparations :2- Heating of Alcohols with P2S5 R-OH + P2S5 R-SH + P2O5CH3-OH + P2S5 CH3-SH + P2O5

3- Heating of Alcohols H2S at high temperature pressure, and catalyst:

R-OH + H2S R-SH + H2O 27Chemical Properties:1- With alkali metals:2R-SH + 2 Na 2 R-SNa + H2 2 C2H5 SH + 2 Na 2 C2H5 SNa + H2 sod. Ethyl mercaptide

2- with Aldehyde : S-C2H5CH3CHO + 2C2H5SH HCl CH3CH + H2O mercaptal S-C2H5

Amines

N: 1s22s22px12py12pz1

Structures of aminessp3-hybridsp3-sp3 hybridized orbitals overlapCN NH sp3hybridized -1s orbitals overlap

Tertiary amines with 3 different groups:Interconversion of amine enantiomers

N: 1s22s22px12py12pz1

PyramidAmines are derivatives of ammonia NH3.

Contain N attached to one or more alkyl (Aliphatic amine) or aromatic groups (Aromatic amine). The shape around the nitrogen is pyrimidal and there is a lone pair of electrons on the nitrogen

CH3-NH2 CH3-NH-CH3 Structure and Classification of Amines-NH2 amino group+

NH2Structure and Classification of AminesAmines can be classified as 1, 2 or 3, just like carbons, based on how many alkyl groups are attached to the nitrogen

Amines are classified into three groups:

depending on the number of carbon groups bonded to nitrogen. CH3 CH3 CH3NH2 CH3NH CH3NCH3AminesPrimary 1Secondary 2Tertiary 3Naming AminesThe same method as we did for alcohols.

Drop the final -e of the parent alkane and replace it by amine.

- Use a number to locate the amino group (-NH2) on the parent chain.

IUPAC name 1 amines

CH3-CH-CH3NH22-propanamineCH3-CH-CH-CH3NH2Cl3-chloro-2-butanamine1,6-hexanediamine1231234123456Naming AminesTake the largest group bonded to nitrogen as the parent amine.Name the smaller group(s) bonded to nitrogen, and show their locations on nitrogen by using the prefix N.IUPAC name 2 and 3 amines

anilineCH3-N-CH2-CH3CH3N,N-Dimethylethanamine

Methods of Preparations1-Alkylation of ammonia

The reaction of ammonia with an alkyl halide leads to the formation of a primary amine. The primary amine that is formed can also react with the alkyl halide, which leads to a disubstituted amine that can further react to form a trisubstituted amine. Therefore, the alkylation of ammonia leads to a mixture of products

2) Catalytic reduction of Alkyl cyanides ( nitriles) CH3CN H2/Ni CH3CH2NH2 (ethyl amine) 3) Hoffmann degradation reaction Of Amide

4-The Gabriel synthesis of primary amines

Reagent:

Potassium salt of Phthalimide

Imide

Primary alkyl halide, SN2

CO2NaCO2NaCO2HCO2HNaOH/H2OHCl /H2O+ R-NH2+ R-NH3Cl-5- Reductive amination:

Imine

1o Amine23Physical properties of AminesThey have unpleasant odors (rotting fish like ammonia).

Amines solutions are basic (ammonia or died fish odor)

They are polar compounds; Difference in electronegativity between N - H (3.0 2.1 = 0.9)

4- 1 and 2 amines have hydrogen bonds (N-H).

Weaker than alcohols (O-H). 3 amines do not form hydrogen bonds (no H atom).

Physical properties:5- 1 , 2 amine can form H bond So their MP > alkane of similar M.Wt (B.P Amine > Alkane)

6-Boiling points: Hydrocarbons< Amines < Alcohols

7- Almost soluble