Alkaloids are a class of occurring organic compounds that contain basic nitrogen atoms. This group includes some related compounds with neutral and weakly acidic properties; some synthetic compounds of similar structure may be termed alkaloids. In addition to carbon and nitrogen, alkaloids may contain oxygen, sulfur and, more other elements such as chlorine and phosphorus. Alkaloids are produced by a large variety of organisms including bacteria, fungi and animals, they can be purified from crude extracts of these organisms by acid-base extraction. Alkaloids have a wide range of pharmacological activities including antimalarial, anticancer, vasodilatory, analgesic and antihyperglycemic activities. Many have found use as starting points for drug discovery. Other alkaloids possess psychotropic and stimulant activities, have been used in entheogenic rituals or as recreational drugs. Alkaloids can be toxic too. Although alkaloids act on a diversity of metabolic systems in humans and other animals, they uniformly evoke a bitter taste.
The boundary between alkaloids and other nitrogen-containing natural compounds is not clear-cut. Compounds like amino acid peptides, nucleotides, nucleic acid and antibiotics are not called alkaloids. Natural compounds containing nitrogen in the exocyclic position are classified as amines rather than as alkaloids; some authors, consider alkaloids a special case of amines. The name "alkaloids" was introduced in 1819 by the German chemist Carl Friedrich Wilhelm Meißner, is derived from late Latin root alkali and the suffix -οειδής – "like". However, the term came into wide use only after the publication of a review article by Oscar Jacobsen in the chemical dictionary of Albert Ladenburg in the 1880s. There is no unique method of naming alkaloids. Many individual names are formed by adding the suffix "ine" to the genus name. For example, atropine is isolated from the plant Atropa belladonna. Where several alkaloids are extracted from one plant their names are distinguished by variations in the suffix: "idine", "anine", "aline", "inine" etc.
There are at least 86 alkaloids whose names contain the root "vin" because they are extracted from vinca plants such as Vinca rosea. Alkaloid-containing plants have been used by humans since ancient times for therapeutic and recreational purposes. For example, medicinal plants have been known in the Mesopotamia at least around 2000 BC; the Odyssey of Homer referred to a gift given to Helen by the Egyptian queen, a drug bringing oblivion. It is believed. A Chinese book on houseplants written in 1st–3rd centuries BC mentioned a medical use of Ephedra and opium poppies. Coca leaves have been used by South American Indians since ancient times. Extracts from plants containing toxic alkaloids, such as aconitine and tubocurarine, were used since antiquity for poisoning arrows. Studies of alkaloids began in the 19th century. In 1804, the German chemist Friedrich Sertürner isolated from opium a "soporific principle", which he called "morphium" in honor of Morpheus, the Greek god of dreams; the term "morphine", used in English and French, was given by the French physicist Joseph Louis Gay-Lussac.
A significant contribution to the chemistry of alkaloids in the early years of its development was made by the French researchers Pierre Joseph Pelletier and Joseph Bienaimé Caventou, who discovered quinine and strychnine. Several other alkaloids were discovered around that time, including xanthine, caffeine, nicotine, colchicine and cocaine; the development of the chemistry of alkaloids was accelerated by the emergence of spectroscopic and chromatographic methods in the 20th century, so that by 2008 more than 12,000 alkaloids had been identified. The first complete synthesis of an alkaloid was achieved in 1886 by the German chemist Albert Ladenburg, he produced coniine by reacting 2-methylpyridine with acetaldehyde and reducing the resulting 2-propenyl pyridine with sodium. Compared with most other classes of natural compounds, alkaloids are characterized by a great structural diversity. There is no uniform classification; when knowledge of chemical structures was lacking, botanical classification of the source plants was relied on.
This classification is now considered obsolete. More recent classifications are based on similarity of the carbon biochemical precursor. However, they require compromises in borderline cases. Alkaloids are divided into the following major groups: "True alkaloids" contain nitrogen in the heterocycle and originate from amino acids, their characteristic examples are atropine and morphine. This group a
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules; the production of many man-made chemicals such as drugs, food additives, fabrics depend on organic reactions. The oldest organic reactions are combustion of organic fuels and saponification of fats to make soap. Modern organic chemistry starts with the Wöhler synthesis in 1828. In the history of the Nobel Prize in Chemistry awards have been given for the invention of specific organic reactions such as the Grignard reaction in 1912, the Diels-Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005. Organic chemistry has a strong tradition of naming a specific reaction to its inventor or inventors and a long list of so-called named reactions exists, conservatively estimated at 1000.
A old named reaction is the Claisen rearrangement and a recent named reaction is the Bingel reaction. When the named reaction is difficult to pronounce or long as in the Corey-House-Posner-Whitesides reaction it helps to use the abbreviation as in the CBS reduction; the number of reactions hinting at the actual process taking place is much smaller, for example the ene reaction or aldol reaction. Another approach to organic reactions is by type of organic reagent, many of them inorganic, required in a specific transformation; the major types are oxidizing agents such as osmium tetroxide, reducing agents such as Lithium aluminium hydride, bases such as lithium diisopropylamide and acids such as sulfuric acid. Reactions are classified by mechanistic class; these classes are polar and pericyclic. Polar reactions are characterized by the movement of electron pairs from a well-defined source to a well-defined sink. Participating atoms undergo changes in charge, both in the formal sense as well as in terms of the actual electron density.
The vast majority of organic reactions fall under this category. Radical reactions are characterized by species with unpaired electrons and the movement of single electrons. Radical reactions are further divided into chain and nonchain processes. Pericyclic reactions involve the redistribution of chemical bonds along a cyclic transition state. Although electron pairs are formally involved, they move around in a cycle without a true source or sink; these reactions require the continuous overlap of participating orbitals and are governed by orbital symmetry considerations. Of course, some chemical processes may involve steps from two of these categories, so this classification scheme is not straightforward or clear in all cases. Beyond these classes, transition-metal mediated reactions are considered to form a fourth category of reactions, although this category encompasses a broad range of elementary organometallic processes, many of which have little in common. Factors governing organic reactions are the same as that of any chemical reaction.
Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals and carbanions. An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions; the stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by the Zaitsev's rule. Organic reactions are important in the production of pharmaceuticals. In a 2006 review it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon-carbon bond and 10% involved functional group interconversions. There is no limit to the number of possible organic reactions and mechanisms.
However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types; some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway; this overview isn't intended to include every single organic reaction. Rather, it is intended to cover the basic reactions. In condensation reactions a small molecule water, is split off when two reactants combine in a chemical reaction; the opposite reaction, when water is consumed in a reaction, is called hydrolysis. Many polymerization reactions are derived from organic reactions, they are divided into addition polymerizations and step-growth polymerizations. In general the stepwise progression of reaction mechanisms can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition to intermediates and products.
Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group, formed as a result of this reaction. For example, in the Fries rearrangement the reactant is an ester and the reaction product an alcohol. An overview of functional g
Royal Society of Chemistry
The Royal Society of Chemistry is a learned society in the United Kingdom with the goal of "advancing the chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Royal Institute of Chemistry, the Faraday Society, the Society for Analytical Chemistry with a new Royal Charter and the dual role of learned society and professional body. At its inception, the Society had a combined membership of 34,000 in the UK and a further 8,000 abroad; the headquarters of the Society are at Burlington House, London. It has offices in Thomas Graham House in Cambridge where RSC Publishing is based; the Society has offices in the United States at the University City Science Center, Philadelphia, in both Beijing and Shanghai and Bangalore, India. The organisation carries out research, publishes journals and databases, as well as hosting conferences and workshops, it is the professional body for chemistry in the UK, with the ability to award the status of Chartered Chemist and, through the Science Council the awards of Chartered Scientist, Registered Scientist and Registered Science Technician to suitably qualified candidates.
The designation FRSC is given to a group of elected Fellows of the society who have made major contributions to chemistry and other interface disciplines such as biological chemistry. The names of Fellows are published each year in The Times. Honorary Fellowship of the Society is awarded for distinguished service in the field of chemistry; the president is elected biennially and wears a badge in the form of a spoked wheel, with the standing figure of Joseph Priestley depicted in enamel in red and blue, on a hexagonal medallion in the centre. The rim of the wheel is gold, the twelve spokes are of non-tarnishable metals; the current president is Dame Carol V. Robinson. Past presidents of the society have been: The following are membership grades with post-nominals: Affiliate: The grade for students and those involved in chemistry who do not meet the requirements for the following grades. AMRSC: Associate Member, Royal Society of Chemistry The entry level for RSC membership, AMRSC is awarded to graduates in the chemical sciences.
MRSC: Member, Royal Society of Chemistry Awarded to graduates with at least 3 years' experience, who have acquired key skills through professional activity FRSC: Fellow of the Royal Society of Chemistry Fellowship may be awarded to nominees who have made an outstanding contribution to chemistry. HonFRSC: Honorary Fellow of the Society Honorary Fellowship is awarded for distinguished service in the field of chemistry. CChem: Chartered Chemist The award of CChem is considered separately from admission to a category of RSC membership. Candidates need to be MRSC or FRSC and demonstrate development of specific professional attributes and be in a job which requires their chemical knowledge and skills. CSci: Chartered Scientist The RSC is a licensed by the Science Council for the registration of Chartered Scientists. EurChem: European Chemist The RSC is a member of the European Communities Chemistry Council, can award this designation to Chartered Chemists. MChemA: Mastership in Chemical Analysis The RSC awards this postgraduate qualification, the UK statutory qualification for practice as a Public Analyst.
It requires candidates to submit a portfolio of suitable experience and to take theory papers and a one-day laboratory practical examination. The qualification GRSC was awarded from 1981 to 1995 for completion of college courses equivalent to an honours chemistry degree and overseen by the RSC, it replaced the GRIC offered by the Royal Institute of Chemistry. The society is organised around 9 divisions, based on subject areas, local sections, both in the United Kingdom and overseas. Divisions cover broad areas of chemistry but contain many special interest groups for more specific areas. Analytical Division for analytical chemistry and promoting the original aims of the Society for Analytical Chemistry. 12 Subject Groups. Dalton Division, named after John Dalton, for inorganic chemistry. 6 Subject Groups. Education Division for chemical education. 4 Subject Groups. Faraday Division, named after Michael Faraday, for physical chemistry and promoting the original aims of the Faraday Society. 14 Subject Groups.
Organic Division for organic chemistry. 6 Subject Groups. Chemical Biology Interface Division. 2 Subject Groups. Environment and Energy Division. 3 Subject Groups. Materials Chemistry Division. 4 Subject Groups. Industry and Technology Division. 13 Subject Groups. There are 12 subjects groups not attached to a division. There are 35 local sections covering the United Ireland. In countries of the Commonwealth of Nations and many other countries there are Local Representatives of the society and some activities; the society is a not-for-profit publisher: surplus made by its publishing business is invested to support its aim of advancing the chemical sciences. In addition to scientific journals, including its flagship journals Chemical Communications, Chemical Science and Chemical Society Reviews, the society publishes: Education in Chemistry for teachers. A free online journal for chemistry educators, Chemistry Education Research and Practice. A general chemistry magazine Chemistry World, sent monthly to all members of the Society throughout the world.
The editorial board consists of 10 industrial chemists. It was first published in January 2004, it replaced C
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group replaced by a nitrogen atom, it is a flammable, weakly alkaline, water-soluble liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless; the pyridine ring occurs in many important compounds, including agrochemicals and vitamins. Pyridine was produced from coal tar. Today it is synthesized on the scale of about 20,000 tonnes per year worldwide; the molecular electric dipole moment is 2.2 debyes. Pyridine is diamagnetic and has a diamagnetic susceptibility of −48.7 × 10−6 cm3·mol−1. The standard enthalpy of formation is 100.2 kJ·mol−1 in the liquid phase and 140.4 kJ·mol−1 in the gas phase. At 25 °C pyridine has a viscosity of 0.88 mPa/s and thermal conductivity of 0.166 W·m−1·K−1. The enthalpy of vaporization is 35.09 kJ · mol − 1 at normal pressure. The enthalpy of fusion is 8.28 kJ·mol−1 at the melting point. The critical parameters of pyridine are pressure 6.70 MPa, temperature 620 K and volume 229 cm3·mol−1.
In the temperature range 340–426 °C its vapor pressure p can be described with the Antoine equation log 10 p = A − B C + T where T is temperature, A = 4.16272, B = 1371.358 K and C = −58.496 K. Akin to benzene, pyridine ring forms a C5N hexagon. Electron localization in pyridine is reflected in the shorter C–N ring bond, whereas the carbon–carbon bonds in the pyridine ring have the same 139 pm length as in benzene; these bond lengths lie between the values for the single and double bonds and are typical of aromatic compounds. Pyridine crystallizes in an orthorhombic crystal system with space group Pna21 and lattice parameters a = 1752 pm, b = 897 pm, c = 1135 pm, 16 formula units per unit cell. For comparison, crystalline benzene is orthorhombic, with space group Pbca, a = 729.2 pm, b = 947.1 pm, c = 674.2 pm, but the number of molecules per cell is only 4. This difference is related to the lower symmetry of the individual pyridine molecule. A trihydrate is known; the optical absorption spectrum of pyridine in hexane contains three bands at the wavelengths of 195 nm, 251 nm and 270 nm.
The 1H nuclear magnetic resonance spectrum of pyridine contains three signals with the integral intensity ratio of 2:1:2 that correspond to the three chemically different protons in the molecule. These signals originate from γ-proton and β-protons; the carbon analog of pyridine, has only one proton signal at 7.27 ppm. The larger chemical shifts of the α- and γ-protons in comparison to benzene result from the lower electron density in the α- and γ-positions, which can be derived from the resonance structures; the situation is rather similar for the 13C NMR spectra of pyridine and benzene: pyridine shows a triplet at δ = 150 ppm, δ = 124 ppm and δ = 136 ppm, whereas benzene has a single line at 129 ppm. All shifts are quoted for the solvent-free substances. Pyridine is conventionally detected by mass spectrometry methods; because of the electronegative nitrogen in the pyridine ring, the molecule is electron deficient. It, enters less into electrophilic aromatic substitution reactions than benzene derivatives.
Correspondingly pyridine is more prone to nucleophilic substitution, as evidenced by the ease of metalation by strong organometallic bases. The reactivity of pyridine can be distinguished for three chemical groups. With electrophiles, electrophilic substitution takes place where pyridine expresses aromatic properties. With nucleophiles, pyridine reacts at positions 2 and 4 and thus behaves similar to imines and carbonyls; the reaction with many Lewis acids results in the addition to the nitrogen atom of pyridine, similar to the reactivity of tertiary amines. The ability of pyridine and its derivatives to oxidize, forming amine oxides, is a feature of tertiary amines; the nitrogen center of pyridine features a basic lone pair of electrons. This lone pair does not overlap with the aromatic π-system ring pyridine is a basic, having chemical properties similar to those of tertiary amines. Protonation gives pyridinium, C5H5NH+; the pKa of the conjugate acid is 5.25. The structures of pyridine and pyridinium are identical.
The pyridinium cation is isoelectronic with benzene. Pyridinium p-toluenesulfonate is an illustrative pyridinium salt. In addition to protonation, pyridine undergoes N-centered alkylation, N-oxidation. Pyridine has a conjugated system of six π electrons; the molecule is planar and, follows the Hückel criteria for aromatic systems. In contrast to benzene, the electron density is not evenly distributed over the ring, reflecting the negative inductive effect of the nitrogen atom. For this reason, pyridine has a dipole moment and a weaker resonant stabilization than benzene (re
The Knoevenagel condensation reaction is an organic reaction named after Emil Knoevenagel. It is a modification of the aldol condensation. A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated; the product is an α,β-unsaturated ketone. In this reaction the carbonyl group is a ketone; the catalyst is a weakly basic amine. The active hydrogen component has the form Z–CH2-Z or Z–CHR–Z for instance diethyl malonate, Meldrum's acid, ethyl acetoacetate or malonic acid, or cyanoacetic acid. Z–CHR1R2 for instance nitromethane.where Z is an electron withdrawing functional group. Z must be powerful enough to facilitate deprotonation to the enolate ion with a mild base. Using a strong base in this reaction would induce self-condensation of the aldehyde or ketone; the Hantzsch pyridine synthesis, the Gewald reaction and the Feist–Benary furan synthesis all contain a Knoevenagel reaction step.
The reaction led to the discovery of CS gas. With malonic compounds the reaction product can lose a molecule of carbon dioxide in a subsequent step. In the so-called Doebner modification the base is pyridine. For example, the reaction product of acrolein and malonic acid in pyridine is trans-2,4-Pentadienoic acid with one carboxylic acid group and not two. A Knoevenagel condensation is demonstrated in the reaction of 2-methoxybenzaldehyde 1 with the thiobarbituric acid 2 in ethanol using piperidine as a base; the resulting enone 3 is a charge transfer complex molecule. The Knoevenagel condensation is a key step in the commercial production of the antimalarial drug lumefantrine: The initial reaction product is a 50:50 mixture of E and Z isomers but because both isomers equilibrate around their common hydroxyl precursor, the more stable Z-isomer can be obtained. A multicomponent reaction featuring a Knoevenagel condensation is demonstrated in this MORE synthesis with cyclohexanone, malononitrile and 3-amino-1,2,4-triazole: The Weiss–Cook reaction consists in the synthesis of cis-bicyclooctane-3,7-dione employing an acetonedicarboxylic acid ester and a diacyl.
The mechanism operates in same way as the Knoevenagel condensation: Malonic ester synthesis Aldol condensation Nitroalkene Iminocoumarin
In organic chemistry, AD-mix is a commercially available mixture of reagents that acts as an asymmetric catalyst for various chemical reactions, including the Sharpless asymmetric dihydroxylation of alkenes. The two letters AD, stand for asymmetric dihydroxylation; the mix is available in two variations, "AD-mix α" and "AD-mix β" following ingredient lists published by Barry Sharpless. The mixes contain: Potassium osmate K2OsO24 as the source of Osmium tetroxide Potassium ferricyanide K3Fe6, the re-oxidant in the catalytic cycle Potassium carbonate A chiral ligand: AD-mix α contains 2PHAL, the phthalazine adduct with dihydroquinineAD-mix β contains 2PHAL, the phthalazine adduct with dihydroquinidine Catalytic Asymmetric Dihydroxylation of Alkenes at Imperial College London Link
Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, not consumed in the catalyzed reaction and can continue to act repeatedly. Because of this, only small amounts of catalyst are required to alter the reaction rate in principle. In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst reacts to form a temporary intermediate, which regenerates the original catalyst in a cyclic process. A substance which provides a mechanism with a higher activation energy does not decrease the rate because the reaction can still occur by the non-catalyzed route. An added substance which does reduce the reaction rate is not considered a catalyst but a reaction inhibitor. Catalysts may be classified as either heterogeneous. A homogeneous catalyst is one whose molecules are dispersed in the same phase as the reactant's molecules.
A heterogeneous catalyst is one whose molecules are not in the same phase as the reactant's, which are gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are considered as a third category. In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations; the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have a lower activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature and for the same reactant concentrations. However, the detailed mechanics of catalysis is complex. Catalysts may bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to reactive forms, such as chemisorbed hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions are typical chemical reactions. The catalyst participates in this slowest step, rates are limited by amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or sublimate in a solid–gas system; the production of most industrially important chemicals involves catalysis. Most biochemically significant processes are catalysed.
Research into catalysis is a major field in applied science and involves many areas of chemistry, notably organometallic chemistry and materials science. Catalysis is relevant to many aspects of environmental science, e.g. the catalytic converter in automobiles and the dynamics of the ozone hole. Catalytic reactions are preferred in environmentally friendly green chemistry due to the reduced amount of waste generated, as opposed to stoichiometric reactions in which all reactants are consumed and more side products are formed. Many transition metals and transition metal complexes are used in catalysis as well. Catalysts called. A catalyst works by providing an alternative reaction pathway to the reaction product; the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates oxygen, as shown below. 2 H2O2 → 2 H2O + O2This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow.
In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available. This reaction is affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms. Upon the addition of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly; this effect is seen by the effervescence of oxygen. The manganese dioxide is not consumed in the reaction, thus may be recovered unchanged, re-used indefinitely. Accordingly, manganese dioxide catalyses this reaction. Catalytic activity is denoted by the symbol z and measured in mol/s, a unit, called katal and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the catalyst under certain conditions, in relation to a specific chemical reaction. Catalytic activity of one katal of a catalyst means one mole of that catalyst will catalyse 1 mole of the reactant to product in one second. A catalyst may and will have different catalytic activity for di