Introduction:
Alkanol are the group of compounds in which the hydrogen atom(s) of alkanes have been substituted with the hydroxyl (-OH) functional group. Alkanols are usually termed to as 'alcohols'. We are as well familiar that the general formula of Alkanols is CnH2n+1OH and are named by replacing the 'e' of the alkane name via 'ol'. For example - methanol and ethanol from methane and ethane.
Fig: Methanol and ethanol
A simple general representation for Alkanols is R-OH; here 'R' symbolizes an alkyl group. Whenever essential, the position of the -OH group is illustrated numerically, example: propanol. The carbon atoms are numbered in the longest chain. The position of the OH group finds out the numbers. Let us study the structures shown below.
Fig: Alkanols
The hydroxyl group is one of the most significant functional groups of naturally occurring molecules like carbohydrates and nucleic acids. These are complex alkanols however the main concern are simple alkanols which are made up from petroleum-derived hydrocarbons.
Classification of Alkanols:
Alkanols are categorized as primary, secondary or tertiary based on whether the OH functional group is linked to a primary, secondary or tertiary carbon atom, example:
Fig: Classification of Alkanols
Sources of Alkanols:
General methods of preparation:
(a) Hydrolysis of halogenoalkanes or alkyl halides:
Alkyl halides are the compounds made by replacing one of the hydrogen of an alkane with a halogen (Cl or Br or I). Whenever alkyl halides are treated by dilute aqueous sodium hydroxide, the halogen is substituted by - OH groups therefore making an alkanol.
R-Cl + Na+ + OH- → R-OH + NaCl
Example: CH3CH2Cl + NaOH → CH3CH2-OH + NaCl
Ethyl chloride Ethanol
(b) Hydration of alkenes:
The Alkenes react with steam whenever passed over phosphoric (v) acid catalyst at 300°C and 70 atmosphere. For illustration:
CH2 = CH2 + H2O → (H3PO4 at 300oc + 70 atms) → CH3-CH2-OH
The method, as illustrated in the equation, is mainly used industrially for the production of ethanol and some higher alkanols.
Manufacture of alkanols:
a) Methanol: Methanol is mainly made up from mixture of carbon (II) oxide and hydrogen (that is, obtained from either water gas or synthesis gas) in the presence of a catalyst.
C(coke) + H2O(g) → CO + H2 (water gas)
CH4 (natural gas) + H2O (g) → CO + 3H2 (synthesis gas)
CO + 2H2 → (ZnO + Cr2O3 at 400oc and 300 atm) → CH3OH
(b) Ethanol:
- From ethene: The main source of ethanol industrially is through hydration of alkenes as illustrated above.
- By fermentation: The fermentation method of obtaining ethanol from starch materials is still admired.
Fermentation is basically the decomposition of complex organic compounds example: carbohydrates, into simpler compounds via the action of enzymes.
Materials like - sugar, guinea-corn, rice, cassava, maize, potatoes, wheat, barley and so on can be employed as the source of glucose from which the ethanol is derived.
Malt, made up from partially germinated barley, is added and then kept at around 50°C for one hour. The enzyme diastase, present in the malt, catalyses the conversion of starch to the maltose.
2(C6H10O5)n + nH2O → (diastase) → nC12H22O11
Starch maltose
The yeast is then added at room temperature. This causes fermentation, the enzyme maltase in the yeast, transforms the maltose to glucose and the other enzyme zymase in yeast, then decomposes the glucose into ethanol and carbon (iv) oxide.
C12H22O11 (aq) + H2O → (maltase) → 2C6H12O6 (aq)
Glucose
C6H12O6 → (zymase) → 2C2H5OH + 2CO2
ethanol
C12H22O11 + H2O → (invertase) → C6H12O6 + C6H12O6 → (zymase) → 4C2H5OH + 4CO2
Glucose Fructose
(c) Purification of ethanol:
The ethanol achieved from the fermentation method can only provide a maximum concentration of 18%, as the yeast cells die above this concentration. For commercial use, ethanol is needed in different compositions and to accomplish further concentration and purification, fractional distillation is used.
For the alcoholic beverages, different concentrations of ethanol are employed and their flavor differs with raw material fermented. The table illustrated below represents the percentage of ethanol and the method of preparation.
Table: Kinds of alcoholic beverages
Raw material
Alcohol beverage
% Ethanol (v/u)
Method of preparation
Barley, Wheat
Beer e.g. star
3 - 8
Fermentation
Grapes/Rice
Wines
8 - 18
Barley, Wheat, Grapes
Whisky/Spirit/Brandy
30 - 60
Fermentation & Distillation
The commercial ethanol is sold as pure spirit or rectified spirit or methylated spirit having 95% ethanol. Whenever sold to the public, 5% methanol, which is toxic, is added to prevent it being used as a drink.
Uses of ethanol:
1) This is used as solvent for resins, polishes, varnishes, liquid soaps, perfumes, drugs and paints.
2) It is employed as a fuel, either by itself or mixed by petrol, in rockets and racing cars.
3) It is employed as an anti-freeze in the automobile radiator.
4) It is present in numerous alcoholic beverages.
5) It is employed for sterilization and preservation of the specimens and food.
6) It is employed as raw material in the manufacture of chemical example: ethanol, trichloromethane and ethoxyethane.
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online chemistry tutoring. Chat with us or submit request at [email protected]
Production and energy flow tutorial all along with the key concepts of Measurement of productivity, biomass of photosynthesizing cells, Amount of light attenuating materials, abundance and frequency range of light
Interpretation of a Mass Spectrum tutorial all along with the key concepts of Rules employed in the Interpretation of Mass Spectra, Mass Spectrum of Toluene and Examples of Mass Spectra Interpretation
Theory and lecture notes of Public Goods all along with the key concepts of public goods, Free Rider Problem, Optimal Output Decision of Public Good, Externalities and Public Goods. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Public Goods.
www.tutorsglobe.com offers acidity of a c–h homework help, acidity of a c–h assignment help, online tutoring assistance, organic chemistry solutions by online qualified tutor's help.
tutorsglobe.com meiosis-ii assignment help-homework help by online meiosis tutors
theory and lecture notes of theory of p-values all along with the key concepts of p-values, classical approach, p-value approach, homework help and assignment help. tutorsglobe offers homework help, assignment help and tutor’s assistance on theory of p-values.
tutorsglobe.com capital structure assignment help-homework help by online financial management tutors
tutorsglobe.com arthritis assignment help-homework help by online bones and joints tutors
tutorsglobe.com minerals assignment help-homework help by online nutrition tutors
tutorsglobe.com uses of noble gas assignment help-homework help by online noble gases tutors
tutorsglobe.com intermediate microeconomics assignment help-homework help by online microeconomics tutors
Maxwell Relations tutorial all along with the key concepts of Differential forms of thermodynamic potentials, Differential form of internal energy, differential form of Enthalpy, differential of Helmholtz free energy, differential of Gibb's free energy, Four Maxwell Relations of thermodynamics
Theory and lecture notes of Market signaling all along with the key concepts of market signaling, Education as a signal, Educational Signaling Game, Economics of information. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Market signaling.
tutorsglobe.com primary wall assignment help-homework help by online structure of the cell wall tutors
www.tutorsglobe.com offers system analysis to build a new system homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
1963293
Questions Asked
3689
Tutors
1445800
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!