Introduction:
Quinoline was first extracted from the coal tar in the year 1834 by Friedlieb Ferdinand Runge. Coal tar remains the main source of commercial quinoline. This can be synthesized by different methods like the Skraup, Dobner-von Miller Synthesis, Conrad-Limpach, Friedlaender and Pfitzinger synthesis.
Skraup Synthesis of Quinoline:
The Aniline, glycerol, nitrobenzene, iron (II) sulphate and sulphuric acid are mixed and gently heated. The vigorous exothermic reaction takes place that is completed by further heating. After the elimination of residual nitrobenzene by distillation in steam, quinoline is released from the reaction mixture via basification and is isolated by steam-distillation. The result of the purified product is 84 to 91%.
The reaction comprises dehydration of glycerol to propenal (Acrolein), Michael-type addition of aniline to propenal, acid-catalyzed cyclisation and dehydrogenation by nitrobenzene (fig shown below). Iron (II) sulphate acts to moderate the reaction. The propenal itself is not used due to its tendency to polymerize. The success of the reaction based on the rapid addition of aniline to the propenal as it is formed.
Fig: Skraup Synthesis of Quinoline
The synthesis is of broad application particularly for the synthesis of quinoline substituted in the benzene ring. The aniline might have nuclear substituents: ortho- and para-substituted anilines give 8- and 6-substituted quinolines, correspondingly, and meta-substituted anilines provides mixtures of 5- and 7-substituted quinolines, the latter predomination with activating substituents like methoxyl and the former predominating by deactivating substituents like nitro. Propenal might be substituted by 2-butenal providing 2-methylquinolines and by butanone, providing 4-methylquinolines.
The Dobner-von Miller Synthesis:
The reaction employs pre-formed α, β-unsaturated carbonyl compounds rather than acrolein. This is employed to give alkyl and aryl substituents in the 'pyridine' half of the quinoline.
The intermediate β-aminocarbonyl compound can be isolated and this exhibits that the mechanism begins by a conjugate addition. The intermediate might then be subsequently cyclised under a variety of conditions (figure shown below).
Fig: Dobner-von Miller Synthesis
The Conrad-Limpach Synthesis:
β-keto esters react by aniline in each of two manners; at low temperatures reaction takes place at the keto-group to provide an imine and at high temperatures reaction takes place at the ester group to provide an amide. The resultant compounds can each be cyclised to the quinolines (figure shown below).
Fig: Conrad-Limpach Synthesis
The Friedlaender Synthesis:
The o-aminobenzaldehyde is treated by an aldehyde or ketone in a basic medium; formation of the imine is obeyed by dehydrative cyclisation (figure shown below).
Fig: Friedlaender Synthesis
The major problem by this synthesis is that o-aminobenzaldehyde is very unstable, readily undergoing self-condensation. One way of overcoming this is to start rather by an o-nitrobenzaldehyde: acid- or base-catalyzed reaction provides an intermediate that cyclises spontaneously on reduction.
Fig: Variation of Friedlaender Synthesis
The Pfitzinger Synthesis:
This is the modification of Friedlander's method and uses isatin in place of 0-aminobenzaldehyde. Reaction by the base provides o-aminobenzoylformate ion that reacts by an aldehyde or ketone to provide a 4-carboxyquinoline from which the carboxyl group can be eliminated thermally (figure shown below).
Fig: Pfitzinger Synthesis
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 an expert 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]
tutorsglobe.com consumer equilibrium by indifference curve assignment help-homework help by online indifference curve approach tutors
tutorsglobe.com antibiotics and chemotherapy assignment help-homework help by online chemotherapy tutors
www.tutorsglobe.com offers software requirement analysis homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
www.tutorsglobe.com offers Concept of Abstraction homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
tutorsglobe.com shift in demand and supply assignment help-homework help by online equilibrium price tutors
Jet Dyeing Machine tutorial all along with the key concepts of Definition of Jet Dyeing Machine, Types of Jet Dyeing Machine, Key Features of Soft Flow Dyeing Machine, Types of Soft Flow Dyeing Machine, Air flow dyeing machine
www.tutorsglobe.com offers conic section homework help, conic section assignment help, online tutoring assistance, geometry mathematics solutions by online qualified math tutor's help.
Interference by division of Wavefront tutorial all along with the key concepts of Wave motion, Transverse wave and longitudinal wave, Characteristics of waves, Principle of superposition, Young's double slit experiment, Fresnel's Biprism
Chemical methods of controlling Microbial growth tutorial all along with the key concepts of Definition of Disinfection, Antimicrobial Agents, Ideal Antimicrobial Agent or Disinfectant, Chemical Antimicrobial Agents, Phenolics, Alcohols, Halogens and Quaternary Ammonium Compounds
tutorsglobe.com androecium assignment help-homework help by online position of flower tutors
theory and lecture notes of concept of mos transistor all along with the key concepts of mosfet, source, gate, drain, operating modes of mos transistor, accumulation, depletion and inversion. tutorsglobe offers homework help, assignment help and tutor’s assistance on concept of mos transistor.
www.tutorsglobe.com offers other object oriented issues homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
tutorsglobe.com demand functions assignment help-homework help by online choice and utility maximization tutors
www.tutorsglobe.com offers implicit invocation homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
Millman Theorem and Nortons Theorem tutorial all along with the key concepts of Calculation of a Norton equivalent circuit, Ohm's Law and Reciprocity
1958212
Questions Asked
3689
Tutors
1477798
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!