7 Introductory Organic Chemistry

Prof. K. Maharaj Kumari

Contents

1. Introduction
2. Hydrocarbons

                      A. Natural source of hydrocarbons

                  B. Classification of hydrocarbons

                  C. Atmospheric reactions of alkanes

                  D. Atmospheric reactions of alkenes

                                                (i) Reaction with OH. Radical

                                                (ii) Reaction with O3

                                                (iii) Reaction with NO3 radical

3. Aliphatic aldehydes and ketones

                     A. Nomenclature

                 B. Atmospheric reactions of aldehydes and ketones

                                                   (i) Photolysis

                                                   (ii) Reaction with OH˙

4. Alcohols and ethers:

                  A. Nomenclature

                  B. Atmospheric reactions of alcohols:

                                   (i) Reaction with OH radical

5. Aromatic hydrocarbons

                    A. Nomenclature

6. Carboxylic acids

                    A. Nomenclature

                   B. Atmospheric reactions of Carboxylic acids

7. Polyaromatic hydrocarbons

Introduction

   Organic chemistry is the branch which was initiated to understand the chemistry of life. However it soon rose to vast multinational industries that feed, clothe, and cure millions of people without their even being aware of the role of chemistry in their lives. It is the branch of chemistry closest to us, we depend on organic compounds for food, drugs, perfumes etc. Organic chemistry is the study of compounds that contain carbon. Nearly all organic compounds also contain hydrogen; most also contain oxygen, nitrogen, or other elements. The study of organic chemistry encompasses bonding of these atoms into stable molecular structures, and the way in which these structures change in the course of chemical reactions.

   Carbon as an element is unique in the variety of structures it can form. It is unusual because it forms strong, stable bonds to the majority of elements in the periodic table, including itself. However, it is this ability to form bonds to itself that leads to the variety of organic structures leading to a whole branch of organic chemistry, although carbon may make up only 0.2% of the earth’s crust. A variety of organic compounds are emitted into the atmosphere by natural and human activities. They can be divided into two categories namely: primary pollutants and secondary pollutants. The primary pollutants are those that are emitted directly from the sources, eg. Hydrocarbons from automobile exhaust-ethane, ethane, toluene etc. The secondary pollutants are those that are formed in the atmosphere by chemical interactions among the primary pollutants and normal atmospheric constituents and photochemical reactions in the atmosphere eg. Formation of peroxyacyl nitrate (PAN) from hydrocarbons.

Natural source of hydrocarbons:

   Natural sources are the main source of most of the organic compounds in the atmosphere. Atmospheric hydrocarbons produced by living sources are called biogenic hydrocarbons. Vegetation is the most important natural source of non-methane biogenic compounds. Ethylene, C2H4, is released to the atmosphere by a variety of plants. Most of the hydrocarbons emitted predominantly by trees are terpenes. These compounds contain olefinic bonds and hence are most reactive compounds in the atmosphere. Terpenes react rapidly with hydroxyl radical, HO· and with other oxidizing agents in the atmosphere, particularly ozone.

Hydrocarbons:

   The gaseous and volatile liquid hydrocarbons are of particular interest as air pollutants. Hydrocarbons can be saturated or unsaturated, branched or straight-chain, or can have a ring structure as in the case of aromatics or other cyclic compounds. In the saturated class, methane is by far the most abundant hydrocarbon constituting about 40 to 80 percent of total hydrocarbons present in the urban atmosphere. Hydrocarbons predominate among the atmospheric pollutants because of their widespread use in fuels. They enter the atmosphere either directly from the fuel or as by-products of partial combustion of other hydrocarbons, which tend to be unsaturated and relatively reactive. Terpenes are a particular class of volatile hydrocarbons emitted largely by natural sources. These are cyclic non-aromatic hydrocarbons found in pine tar and in other wood sources. Polycyclic aromatic hydrocarbons (PAHs) commonly occur in urban atmospheres up to about 20μg m-3 level. Elevated levels of PAHs are observed in polluted urban atmospheres, in the vicinity of forest fires and burning of coal.

   The hydrocarbons in air by themselves are not harmful; however, they are of concern because they undergo chemical reactions in the presence of sunlight and nitrogen oxides forming photochemical oxidants of which the predominant one is ozone. An atmosphere heavily polluted with automobile exhaust, exposure to intense sunlight and inversion results in formation of photochemical oxidants. This phenomenon is called photochemical smog, which is observed in major big cities of the world like Los Angeles (also called Los Angeles Smog). ‘Smog’ originally meant a combination of smoke and fog prevalent in London and is chemically reducing with high levels of SO2 and is called reducing smog whereas Photochemical Smog is oxidizing having high concentration of oxidants. Hydrocarbons play an important role in several photochemical reactions. The most important photochemical reaction in the atmosphere is photo dissociation of NO2 leading to atomic oxygen the initiator of hydrocarbon reactions.

Formation o f photochemical smog (http://www.geocities.ws/xavier114fch/03/images/03b_03.gif )

   Hydrocarbons undergo heterogeneous reactions on particles in the atmosphere. Dusts composed of metal oxides and charcoal have catalytic effect on organic compounds.

Classification of Hydrocarbons

   These molecules only contain carbon and hydrogen. The hydrocarbons that we are going to look at are called aliphatic compounds. The aliphatic compounds are divided into acyclic compounds (chain structures) and cyclic compounds (ring structures). The chain structures are further divided into structures that contain only single bonds (alkanes), those that contain at least one double bond (alkenes) and those that contain at least one triple bond (alkynes). Cyclic compounds include structures such as the benzene ring.

The saturated hydrocarbons are so named because they cannot react with hydrogen. The saturated hydrocarbons contain only single covalent bonds between their C-C and C-H and include alkanes and cycloalkanes. The unsaturated hydrocarbons have a higher oxidation state and react with hydrogen. The unsaturated hydrocarbons include all of the acyclic and cyclic compounds with one or more double bonds, one or more triple bonds or both.

Alkanes

   Alkanes have general molecular formula CnH2n+2 where n is number of C atoms. They are called ‘paraffins’ which means little affinity as they are generally unreactive. They not only are unreactive to acids, bases and oxidizing agents but do not react with reducing agents because they are already in highly reduced state. Their unreactivity can be a bonus, and alkanes such as pentane and hexane are often used as solvents, especially for purification of organic compounds. All alkanes undergo combustion— methane, propane, and butane are all used as domestic fuels, and petrol is a mixture of alkanes containing largely isooctane.

Atmospheric Reactions of Alkanes

   In the troposphere, alkanes react with OH radicals and, to a much lesser extent, with NO3˙ radicals. Alkanes do not absorb in the actinic region (i.e., at wavelengths >290 nm) and do not react with O3. For alkanes the initial reaction with OH and NO3˙ radicals proceed by initial H-atom abstraction and the subsequent reactions in the troposphere are:

   Under tropospheric conditions alkyl (R˙) radicals react only with O2 to form the corresponding alkyl peroxy (RO2˙) radical.in the troposphere, organic peroxy radicals react with NO, NO2, HO2˙ radicals, organic peroxy radicals, and NO3 radicals, as shown, for example, for RCH2O2˙ (+ M)

   Methane is of concern since it is the most important greenhouse gas after carbon dioxide. Methane is produced by the bacterial action, when dead organic matter is subjected to an oxygen-depleted highly reducing aqueous or terrestrial environment as per the following equation:

   The present tropospheric concentration of methane is about 1.8 ppm and it is increasing at the rate of 0.5% every year. Methane in the troposphere contributes to production of CO and O3, while its photochemical dissociation in the stratosphere is the major source of water vapour. The principal sink for methane decomposition is oxidation via hydroxyl radicals in the troposphere, (CH4 + OH→ CH3• +H2O). This reaction is only the first step of a sequence which transforms methane ultimately to CO and then CO2. The other sinks for methane gas are the reaction with soil and loss to the stratosphere.

Alkenes

   The unsaturated hydrocarbons which contain a double bond between carbon atoms are called alkenes or olefins. The members of this class have the general formula CnH2n. The series is generally called alkene or alkylene or olefin series. Alkenes contain C=C double bonds which impart reactivity to an organic molecule.

IUPAC Nomenclature of Alkenes

   According to the IUPAC system, the name of an alkene is derived by replacing the ending –ane of the corresponding alkane by –ene. Thus

CH2= CH2                  Ethene (Ethane – ane + ene)

CH3- CH2= CH2      Propene (Propane –ane + ene)

Atmospheric Reactions of Alkenes

   Alkenes are emitted into the troposphere from anthropogenic sources (mainly combustion sources such as vehicular exhaust) and from vegetation. In the troposphere alkenes react with OH˙ radical, NO3˙ radical and O3. All three of these reactions are equally important for the transformation process of given alkene in the troposphere.

1. Reaction with OH. radical:

The major pathway involves addition to either carbon atom of the >C=C< bond to form β-hydroxyalkyl radical, as given for 1-butene:

In the troposphere the β-hydroxyalkyl radical react rapidly and solely with o2 to form β-hydroxyalkyl peroxyl radicals. For example:

β-hydroxyalkyl peroxyl radicals react with NO, NO2 (to form thermally labile β-hydroxyalkyl peroxylnitrates), and HO2˙ radicals.

2. Reaction with O3:

O3 initially adds to >C=C< bond to form an energy rich primary ozonide, which rapidly decomposes to form two sets of carbonyl + biradical. The relative importance of two decomposition pathways of primary ozonide depends on the structure of alkene.

3. Reaction with NO3 radical:

The reaction with NO3˙ radical involves initial addition of NO3˙ to form β-nitratoalkyl radical:

β-nitratoalkyl radical reacts with O2 to form β-nitratoalkyl peroxyl radical. β-nitratoalkyl peroxyl radical reacts primarily with NO2 to form thermally unstable peroxynitrates such as CH3CH(OONO2)CH2ONO2 and HO2˙ radicals.

Aliphatic Aldehydes and Ketones

Adehydes: In the IUPAC system , aldehydes are named as alkanals and name of an individual aldehyde is obtained by dropping the terminal ‘e’ of the name of the parent hydrocarbon (having same carbon skelton ) and adding the suffix ‘-al’. Thus HCHO is called methanal, the parent hydrocarbon being methane,

methane – e + al          methanol           ethane – e + al               ethanal

the common and iupac names of some aldehydes are:

Formula	Common name	IUPAC name
HCHO	Formaldehyde	Methanal
CH3CHO	Acetaldehyde	Ethanal
CH3CH2CHO	Propionaldehyde	Propanal
CH3CH2CH2CHO	Butanaldehyde	Butanal
CH3=CHCHO	Acrolein	Propenal

Ketones: According to the common system symmetrical ketones are named as dialkyl ketones. First member of the series is however popularly called acetone. the IUPAC names of ketones is alkanones and the name of an individual member on the system is derived by dropping the final ‘e’ of the parent hydrocarbon (containing same number of c-atoms ) and adding the suffix ‘one’

Formula	Common name	IUPAC name
CH3COCH3	Acetone	Propanone
CH3COCH2CH3	Ethyl methyl ketone	Butanone

   while naming the higher ketones, the position of the carbonyl group has to be assigned. In complex compounds the positional number is inserted before the suffix –one.

Atmospheric Reactions of Aldehydes and Ketones

Carbonyls are very important in the atmospheric chemistry because:

A)They are formed as a result of photochemical oxidation of atmospheric hydrocarbons

B) Some of the carbonyls- formaldehyde, acetaldehyde and acrolein are toxic mutagens, potential carcinogens and eye irritants

C) They are involved in formation of very reactive and harmful free radicals, ozone and peroxyacylnitrates

The simplest and most used carbonyl is HCHO, formaldehyde and is produced in the atmosphere as a result of reaction of oxygen with methoxy radical. It occurs in the atmosphere primarily in the gas phase. Formaldehyde is toxic in nature. It is used in the manufacture of plastics, resins, dyes and explosives.

The major tropospheric reactions of aliphatic aldehydes and ketones are photolysis and reaction with OH˙ radical, NO3˙ radical and HO2˙ radical. Reactions with NO3˙ and HO2˙ radical are of negligible importance in the troposphere.

Photolysis

Photolysis of aldehydes and ketones proceed by the following reactions:

Reaction with OH˙

The reaction of OH˙ radical with aldehyde proceeds mainly by H-atom abstraction from –CHO group.

RCO˙ (acyl) radical react in troposphere with O2 to form an acyl peroxyl (RC(O)OO) ˙ radical,

Acetyl peroxyl radical reacts with NO2 and forms peroxyacetyl nitrate (PAN).

Alcohols and Ethers:

Nomenclature

   According to the common system alcohols are named as ‘alkyl alcohols’, the term alcohol designating the –OH group. Thus the common name of an individual alcohol is obtained by writing the name of the alkyl group R linked to –OH group and then adding ‘alcohol’ as a separate word.

   The position of the alcoholic group and substituent is mentioned with a hyphen and then named as derivative of parent compound.

Atmospheric Reactions of Alcohols:

   Alcohols (saturated and unsaturated) are emitted into the atmosphere by vegetation. These biogenic emissions play an important role in the chemistry of the troposphere. Saturated alcohols have long been used in large quantities as industrial solvents.

   Oxidation of alcohols in the atmosphere involves their reaction with the hydroxyl radical (OH). The corresponding atmospheric half-lives are one week for methanol and t-butyl alcohol, 2.5 days for ethanol, and 8-15 h for other alcohols. Major products are formaldehyde from methanol, acetaldehyde from ethanol, acetone from 2-propanol, 2-butanone and acetaldehyde from 2-butanol and acetone and formaldehyde from t-butyl alcohol.

Reaction with OH Radical: The reaction of saturated alcohols with OH at ambient temperature involves H-atom abstraction from a weaker C-H bond (bond strength = 94 kcal mol -1) rather than from the stronger O-H bond (bond strength = 104 kcal mol-1). H-atom abstraction from C-H bonds, increases from methanol (n = 0) to 1-octanol (n = 7), due to the increasing number of secondary C-H bonds, and the reaction of oh with t-butyl alcohol, which contains only primary (and therefore stronger) C-H bonds, is slower, than that of oh with 1-butanol and 2-butanol which contain weaker secondary and tertiary C-H bonds. H-atom abstraction from tertiary C-H bonds preferentially to H-atom abstraction. From secondary C-H bonds, and H-atom abstraction from secondary C-H bonds preferentially to H-atom abstraction from primary C-H bonds

However, all hydrogens are abstracted with equal probability.

For Ethanol:

The radicals formed in reactions give acetaldehyde, formaldehyde and glycoaldehyde respectively.

While reaction with OH is the only known chemical removal process for alcohols in the atmosphere, physical removal processes should also be considered. These processes, include dry deposition, and, on account of the solubility of alcohols in water, scavenging by hydrometeors (clouds, rain, fog, snow) and by water-containing aerosol particles.

Atmospheric Reactions of Organic Amines

   Organic amines are emitted into the atmosphere through a variety of anthropogenic and natural sources, e.g., animal husbandry operation, industrial waste treatment etc. Organic amines are atmospheric bases as ammonia, and they might participate in nucleation or the growth of new particles through rapid acid–base reactions to form salts in a manner similar to ammonia. The gaseous organic amines are thought to be hazardous and toxic, and furthermore, some of their possible atmospheric oxidation products, for instance nitrosamines (R2NNO), are classified as a carcinogenic compound.

The daytime atmospheric oxidation of organic amines is thought to be initiated by reactions with oh radicals and ozone as like the oxidation of hydrocarbons.

Aromatic Hydrocarbons

Nomenclature: The trivial name for the parent monocyclic arene is benzene. In systematic nomenclature arenes of this class are named as substituted benzenes. In certain compounds benzene is the parent name and substituent is indicated by prefix.

   In other compounds, the substituents and the benzene ring form a new parent name, eg. Methyl benzene is called toluene, hydroxyl benzene is called phenol and amino benzene is called aniline.

The following are the common name of some compounds:

When two substituents are present, the isomers are possible. Their positions are indicated by the prefixes ortho (o-), meta (m-) and para (p-) or by number viz., (1,2), (1,3) and (1,4) respectively.

When more than two groups are present in benzene ring, their positions are numbered. If one of the groups is associated with the common name, the molecule is named as a derivative of the mono-substituted compound numbering from the group written in the common name.

For example:

   High levels of monocyclic aromatic hydrocarbons in the atmosphere are directly linked to anthropogenic activity. Aromatic hydrocarbons play a vital role in urban air pollution. Besides their carcinogenic and mutagenic effects on living organisms and human health, the main importance of aromatic hydrocarbons is their role as precursors for the formation of photo-oxidants and secondary organic aerosols.

   Benzene and alkyl-substituted benzenes such as toluene, xylene and ethyl benzene react with OH˙ and NO3˙ radicals; reaction with OH˙ radical dominates in troposphere. reaction with OH˙ radical proceeds by h-atom abstraction from C-H bond of alkyl substituted group or in case of benzene from C-H bonds of aromatic ring followed by addition of OH˙ radical to aromatic ring to form a hydroxyl cyclohexadienyl or alkyl-substituted hydroxyl cyclohexadienyl radical.

Phenols

   Phenols are a class of aromatic organic compounds consisting of one or more hydroxyl groups attached to an aromatic hydrocarbon group. Phenol is produced naturally as well as synthesized. Phenol is a constituent of coal tar and creosote, decomposing organic material, human and animal wastes. Phenol is also formed during forest fires, and by atmospheric degradation of benzene in the presence of light. In addition, phenol is produced by the body and excreted as a metabolic product independent of external exposure or intake.

   The major sources of phenol and cresol isomers in the atmosphere are from automobile exhaust, wood burning and industrial sources. Phenol is present in the atmosphere as an emission from motor vehicles and as a photo oxidation product of benzene. Phenol can also be released during the combustion of wood, fuel emissions and tobacco. Further, phenols and cresols are emitted in the air from industrial sources. Phenol is used mainly in the manufacturing of phenolic resins, bisphenol and caprolactam. Phenol is a major product of the reaction of oh with benzene in the gas phase, similarly, cresol is produced from the reaction of the OH radical with toluene. Phenols, cresols and dimethylphenols react with OH˙ radical, NO3˙ radical and O3, but reaction with O3 is slow. The OH˙ radical reactions are analogous to the reactions of the OH˙ radical with aromatic hydrocarbons in that reaction proceeds by H-atom abstraction from C-H bond of aromatic ring.

   Reaction with NO3˙ proceeds with initial addition of NO3˙ to aromatic ring, followed by abstraction of H-atom from O-H bond to form phenoxy radical. This phenoxy radical adds with NO2 to form o-nitrophenol.

Halogen Derivatives in the Atmosphere

   Compounds having general formula R-X, where r is an alkyl group or a substituted alkyl or cycloalkyl group and X is a halogen atom (F,Cl,Br, I) are called alkyl halides. Alkyl halides may be further substituted by halogen atoms for corresponding di-, tri- and tetra-halogen substituted alkanes. For example,

   Halogenated hydrocarbons play an important role in the photochemical processes of atmosphere; they act as source of halogen radicals which catalytically destroys ozone.

   Methyl chloride is the most abundant halocarbon in the atmosphere. The natural sources contribute 80% to 90% of total global methyl chloride. Anthropogenic sources are automobile exhaust, burning of pvc and other surface reactions.

Major sink of tropospheric methyl chloride is attack by OH˙ radicals.

Carboxylic acids in the Atmosphere

   Organic compounds containing carboxyl group (-COOH) are called carboxylic acids. Carboxylic acids containing one, two and three carboxyl groups are known as mono, di, and tricarboxylic acids. These may be aliphatic or aromatic. They may also be further divided saturated, unsaturated and substituted e.g. hydroxy, amino and halosubstituted acids. Some representative members are:

Oxalic Acid             Chloroacetic Acid                       Maleic Acid                                      Citric Acid

   Carboxylic acids are one of the dominant classes of organic compounds found in the atmosphere in a variety of phases and contribute a large fraction (~25%) to the non methane hydrocarbon (NMHC) atmospheric mixture. Sources of carboxylic include anthropogenic and biogenic emissions. Carboxylic acids are formed in atmosphere by photochemical oxidation of other organic compounds in gas phase and by reaction of organic compounds dissolved in aqueous phase. They are present in very small amount in troposphere because of their low vapour pressure and high water solubility.

   In the gas phase formic and acetic acids are the dominant species followed by propionic acid. Because of the presence of two carboxyl groups, the dicarboxylic acids are less volatile and are mostly present in particulate phase in the ambient atmosphere. Amongst them oxalic acid is the dominant species followed by succinic, malonic, maleic, adipic and phthalic acids. Carboxylic acids are present in the tropospheric aqueous phase, particularly in rain samples and also in cloud and fog waters, in snow and even in polar ice samples.

   Hydrocarbons and their degradation products are the major precursors of carboxylic acids in atmospheric gaseous phase, and the principal production mechanisms of these acids, in gas-phase, and comprise: ozone-olefin and peroxy acyl radicals reactions.

Where R1, R2, R3, and R4 are substituents including H, CH3, C2H5, etc.

The energy-rich criegee biradicals yield the corresponding carboxylic acid:

   Dicarboxylic acids are assumed to be produced by tropospheric oxidation of cycloolefins and aliphatic diolefins: gas-to-particle conversion.

   Peroxy acyl radicals (RCO(OO˙)) are produced by atmospheric degradation of volatile organic compounds. The photolysis of partly oxygenated hydrocarbons and their reaction with OH˙ and NO3˙ radicals, followed by rapid addition of O2 molecule, are major sources of these compounds:

Polycyclic Aromatic Hydrocarbons (PAHS)

Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds with two or

More fused aromatic rings of carbon and hydrogen atoms. Some important representative members and structures of PAHs are as shown below:

   They have a relatively low solubility in water, but are highly lipophilic. Most of the PAHs with low vapour pressure in the air are adsorbed on particles. When dissolved in water or adsorbed on particulate matter, PAHs can undergo photodecomposition when exposed to ultraviolet light from solar radiation. In the atmosphere, PAHs can react with pollutants such as ozone, nitrogen oxides and sulfur dioxide, yielding diones, nitro- and dinitro-PAHs, and sulfonic acids, respectively. PAHs may also be degraded by some microorganisms in the soil.

   They are naturally found in coal, coal tars, oil, wood, tobacco and other organic materials. Some types of PAHs are used in medicines and to make dyes, plastics and pesticides. PAHs are released into the environment as the result of the incomplete burning of these materials. PAHs are ubiquitous and can be found in every type of environment. Urban environments (cities) tend to have higher levels of PAHs due to the increased amounts of gas and oil burned as well as the increased use of asphalt and tars on roads and shingles on roofs. Most PAHs enter the environment via the atmosphere from a  variety of combustion processes and pyrolysis sources. Owing to their low solubility and high affinity for particulate matter, they are not usually found in water in notable concentrations. The main source of PAH contamination in drinking-water is usually the coal-tar coating of drinking-water distribution pipes, used to protect the pipes from corrosion. Fluoranthene is the most commonly detected PAH in drinking-water and is associated primarily with coal-tar linings of cast iron or ductile iron distribution pipes. PAHs have been detected in a variety of foods as a result of the deposition of airborne PAHs and in fish from contaminated waters. PAHs are also formed during some methods of food preparation, such as charbroiling, grilling, roasting, frying or baking. For the general population, the major routes of exposure to PAHs are from food and ambient and indoor air. The use of open fires for heating and cooking may increase PAH exposure, especially in developing countries. Where there are elevated levels of contamination by coal-tar coatings of water pipes, PAH intake from drinking-water could equal or even exceed that from food.

   Some of the PAHs are lighter (or a lower molecular weight) and can volatize (evaporate) into the air. These PAHs break down by reacting with sunlight and other chemicals in the air. This generally takes days to weeks. These lighter (low molecular weight) PAHs are less toxic to humans and are not carcinogenic. Heavier or higher molecular weight PAHs do not dissolve in water, but stick to solid particles and settle to the sediments in bottoms of lakes, rivers or streams and take weeks to months to break down in the environment. Microorganisms in soils and sediments are the main cause of breakdown. These heavy PAHs are carcinogenic to lab animals and may be carcinogenic to humans.

   PAHs are hydrophobic compounds and their persistence in the environment is mainly due to their low water solubility and electro-chemical stability. Human exposure to PAHs occurs principally by direct inhalation, ingestion or dermal contact, as a result of the widespread presence and persistence in the urban environment. Benzo(a)pyrene and pyrene are the most important carcinogenic PAHs and are components of combustion processes, coke oven and foundry emissions, cigarette smoke and charcoal-grilled meats. Evidence supports an excess risk of lung cancer in workers exposed to mixtures of PAHs at coke ovens, coal gasification plants, petroleum refineries, aluminium smelters, iron and steel foundries and with bitumen, diesel and asphalt.

References

1. Environmental chemistry by Stanley E Mahanan published by Lewis publishers
2. Environmental chemistry by A. K. De published by New Age international
3. Environmental chemistry by Colin Baird published by W. H. Freeman
4. Modern organic chemistry by M. K. Jain and S. C. Sharma published by Vishal publishers
5. P. Khare, N. Kumar, K. M. Kumari and S.S. Srivastava. Atmospheric formic and acetic acids: An Overview. Reviews of Geophysics, 37(2), 227-248, 1999