Alcohols ethers and phenols contain oxygen with only single bonds
In this chapter you will be introduced to the major organic functional groups that contain oxygen. This includes alcohols, phenols, ethers, aldehydes. Ethers have much lower boiling points as compared to isomeric alcohols since they do not contain intramolecular hydrogen bonding. The boiling. Alcohols, phenols and ethers are the basic compounds for the made up of compounds containing –OH groups. Just bond: In this class of alcohols. BEST ETHEREUM MINING POOL INDIA
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Acidity of substituted phenols: In substituted phenols, the presence of electron withdrawing groups such as nitro group enhances the acidic strength of phenol. This effect is more pronounced when such a group is present at ortho and para positions. It is because electron withdrawing groups lead to effective delocalisation of negative charge in phenoxide ion.
On the other hand, electron releasing groups, such as alkyl groups do not favour the formation of phenoxide ion resulting in decrease in acid strength. For example Cresols are less acidic than phenol but nitrophenols are more acidic than phenol. Reactions of phenols: Following reactions are shown by phenols only.
Hence, electrophile attacks preferentially at the o- and p-positions. Some examples are given below a Nitration: With dilute HNO3 at low temperature K , phenol yields a mixture of ortho and para nitrophenols. Note: o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding. That is why o-Nitrophenol and p-nitrophenol can be separated by steam distillation.
Phenol react with concentrated HNO3to give 2,4,6-trinitrophenol picric acid. When phenol is treated with bromine water, 2,4,6-tribromophenol is formed. Preparation of Ethers: a By dehydration of alcohols This method is suitable for the preparation of ethers having primary alkyl groups only. Mechanism: The formation of ether is a nucleophilic bimolecular reaction SN2 involving the attack of alcohol molecule on a protonated alcohol.
Better results are obtained if the alkyl halide is primary. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide. In case of aromatic ether, the aromatic part should be with phenoxide ion. In case of secondary and tertiary alkyl halides, elimination competes over substitution. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed.
Unlike alcohols, ether molecules are not able to form intermolecular hydrogen bonds. The intermolecular forces existing in their liquid states are weak dipole—dipole forces. The solubility of ethers is due to the ability of their molecules to form hydrogen bond with water molecules.
However, solubility of ethers in water decreases from lower members to higher members. This is because of the relative increase in the hydrocarbon portion of the molecule which decreases the tendency of H-bond formation.
Ethers are appreciably soluble in organic solvents like alcohol, benzene, acetone, etc. This is due to the following reasons: 1. In alcohol, the O-H group is directly bonded to an sp 3 hybridized carbon atom, but in phenol, it is bonded to an sp 2 hybridized carbon.
Due to the greater s-character and electronegativity of sp 2 hybridized carbon, the ease of O-H bond cleavage is greater on phenol and hence it is more acidic than alcohol. The ionization of alcohol and phenol is as follows: The alkoxide ion R-O- formed by the ionization of alcohol is not resonance stabilized.
So the negative charge - is localized on oxygen atom. But the phenoxide ion C 6H5-O formed by the ionization of phenol is resonance stabilized as follows. Due to resonance, the negative charge is delocalized and hence phenoxide ion is more stable which favours the ionization of phenol. The presence of electron withdrawing groups like nitro group at ortho and para positions increases the acidic strength of phenol. It is due to the effective delocalisation of negative charge in phenoxide ion.
On the other hand, electron releasing groups like alkyl groups at these positions decreases the acidic strength of phenol. So cresols are less acidic than phenol. Esterification : Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.
The reaction with carboxylic acid and acid anhydride are carried out in the presence of conc. H 2SO 4. The reaction with acid chloride is carried out in the presence of a base pyridine so as to neutralise HCl formed during the reaction. Acetylation of salicylic acid produces aspirin, which is used as an analgesic.
B Reactions involving cleavage of carbon — oxygen C—O bond in alcohols 1. Reaction with hydrogen halides : Alcohols react with hydrogen halides in presence of anhydrous zinc chloride ZnCl 2 to form alkyl halides. The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another Lucas test.
HCl and anhydrous ZnCl 2. Alcohols are soluble in Lucas reagent while their halides are immiscible and produce turbidity in solution. Tertiary alcohols react with Lucas reagent and form immediate turbidity; secondary alcohols are less reactive and form turbidity within 5 minutes while primary alcohols do not produce turbidity at room temperature. But they give turbidity on heating. Reaction with phosphorus trihalides PX 3 : Alcohols react with phosphorus trihalides to give alkyl halides.
Dehydration : Alcohols undergo dehydration removal of a molecule of water on treating with a protic acid like concentrated H 2SO 4 or H 3PO 4, or catalysts such as anhydrous zinc chloride or alumina to form alkenes. For example ethanol undergoes dehydration by heating it with concentrated H2SO 4 at K, we get ethene. Secondary and tertiary alcohols are dehydrated under milder conditions. Step 1: The alcohol on protonation gives an oxonium ion.
This step is reversible and fast. Step 2: The oxonium ion loses a water molecule and forms a carbocation. This is the slowest step and hence, the rate determining step of the reaction. Step 3: Formation of ethene by elimination of a proton. The acid used in step 1 is released in step 3. Oxidation : Alcohols on oxidation give carbonyl compounds aldehydes and ketones or carboxylic acids depending on the nature of oxidising agent used.
Primary alcohols when oxidized using mild oxidising agent like anhydrous CrO 3, we get aldehydes. But with strong oxidising agents like acidified potassium permanganate or potassium dichromate, carboxylic acids are formed. But in presence of strong oxidising agents KMnO 4 and at high temperature, they first give ketones with lesser number of carbon atoms which on further oxidation give carboxylic acids with still lesser number of carbon atoms.
Reaction with hot copper catalyst Primary alcoholic vapours when passed through hot Cu catalyst at K, undergo dehydrogenation to form aldehydes, while secondary alcohols undergo dehydrogenation to give ketones. Electrophilic Substitution reaction: In phenol, the —OH group attached to the benzene ring donate electron pairs and hence it activates it towards electrophilic substitution. Also, in the resonating structures of phenol, the electron density is greater on ortho and para positions.
So the electrophile enters at these positions. The common electrophilic aromatic substitution reactions taking place in phenol are: a Nitration : Phenol reacts with Conc. Nitric acid to give an yellow precipitate of 2,4,6-trinitrophenol commonly called picric acid. Picric acid can also be prepared by treating phenol first with concentrated sulphuric acid followed by treating with concentrated nitric acid.
HNO 3 at low temperature K. The ortho and para isomers can be separated by steam distillation. The reaction takes place in the absence of Lewis acid catalyst like FeBr3. It is due to the highly activating effect of —OH group attached to the benzene ring. When phenol is treated with bromine water, we get a white precipitate of 2,4,6-tribromophenol.
Reimer-Tiemann reaction : Phenol when treated with chloroform in the presence of sodium hydroxide, followed by acidification, we get salycylaldehyde o-hydroxybenzaldehyde. Thiis reaction is known as Reimer - Tiemann reaction. Reaction with zinc dust : Phenol when heated with Zn dust, we get benzene. Oxidation : When phenol is oxidised with chromic acid we get a conjugated diketone known as benzoquinone.
In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing quinones. Some Commercially Important Alcohols 1. It is manufactured by the catalytic hydrogenation of carbon monoxide at about K temperature and atm pressure and in the presence of ZnO — Cr 2O3 catalyst.
It is highly poisonous in nature. It is used as a solvent in paints, varnishes and for making formaldehyde. It is obtained commercially by the fermentation of sugar. The sugar in molasses, sugarcane or fruits like grapes is converted to glucose and fructose, in the presence of an enzyme, invertase. Glucose and fructose undergo fermentation in the presence of another enzyme, zymase to give ethanol and carbondioxide. Both the enzymes invertase and zymase are produced by yeast. If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid acetic acid , which destroys the taste of alcohol.
It can be concentrated upto Ethanol is a colourless liquid. It is used as a solvent in paint industry and in the preparation of a number of carbon compounds. The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate to give it a colour and pyridine a foul smelling liquid. It is known as denaturation of alcohol and the resulting alcohol is known as denatured spirit.
If methanol is used for denaturation, it is called methylated spirit.
Alcohols ethers and phenols contain oxygen with only single bonds oil and gas well investing in stocks(10.9) Alcohols, Phenols, and Thiols
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|Alcohols ethers and phenols contain oxygen with only single bonds||Brevatoxin A is depicted in Figure 9. However, its use has fallen out of favor since the mids due to concerns that it may increase cellular UV damage, as well as contribute to allergies. All that differs is the complexity of the other carbon group attached. The borderline of solubility occurs at about four carbon atoms per oxygen atom. Hence, alcohol contains two parts, one is the alkyl group R groupand the other one is the hydroxyl group OH.|
|1988 economist magazine bitcoin||If the nitrogen is attached only to one carbon, the functional group is a primary amine. If it is attached to three carbons, it is a tertiary amine. Again, these can be either alkyl groups or ones containing benzene rings. Concentrated phenol is toxic and can harm skin with next to no aggravation. However, because it is highly flammable and has the added disadvantage of causing nausea, it has been replaced by newer inhalant anesthetics, including the fluorine-containing compounds halothane, and the halogenated ethers, desflurane, isoflurane, and sevoflurane. Esters An ester is an organic compound that is a derivative of a carboxylic acid in which the hydrogen atom of the hydroxyl group has been replaced with an alkyl group.|
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|Best crypto forecast site||Table 9. Because of its reactivity, it is difficult to handle in the gaseous state. Similarly, phosphines have the suffix "-phosphine" instead of "-amine". Provide names for the following branched alkanes. Notice how subtle differences in structure can cause drastic changes in biological activity. For example, the ester, methyl salicylate is also known as the oil of wintergreen Figure 9.|
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