G.Z. Raskil'dina HYDROCARBONS G.Z. Raskil'dina G.Z. Raskil'dina AND THEIR DERIVATIVES HYDROCARBONS HYDROCARBONS AND THEIR DERIVATIVES AND THEIR DERIVATIVES Ufa Publishing house of USPTU 2020 Ufa Publishing house of USPTU 2020 MINISTRY OF SCIENCE AND HIGHER EDUCATION OF THE RUSSIAN FEDERATION FEDERAL STATE BUDGETARY EDUCATIONAL INSTITUTION HIGHER EDUCATION «UFA STATE PETROLEUM TECHNICAL UNIVERSITY» G.Z. Raskil’dina HYDROCARBONS AND THEIR DERIVATIVES Textbook Ufa Publishing house of USPTU 2020 UDC 547-3, 547-022.1 BBK 24.234-236 R 24 Approved by the Editorial Board of USPTU as a textbook Reviewers: Head of the laboratory of heteroatomic compounds of Institute of petrochemistry and catalysis, Ufa Federal Research Center of Russian Academy of Sciences Professor, Doctor of Chemistry sciences A.G. Ibrahimov Professor of the Department of organic and bioorganic chemistry, Bashkir State. University, Doctor of Chem. sciences E.R. Latypova Raskil’dina, G.Z. R 24 Hydrocarbons and their derivatives: textbook / G.Z. Raskil’dina. ‒ Ufa: Publishing house of USPTU, 2020. – 58 p. ISBN 978-5-7831-1896-8 The textbook is compiled on the basis of the discipline program «Chemistry of oil and gas», aimed at a student of a technical university. It consists of sections on the topic «Hydrocarbons and their derivatives». The chapters contain reaction schemes that contribute to a deeper perception of the material and facilitate its study, at the end of the manual ‒ questions and tasks necessary to assess the level of assimilation of the material. The manual is necessary for students of the groups BGRi, BGBi, BSTi, BMTi and other specialties studying the discipline «Chemistry of oil and gas» in English. UDC 547-3, 547-022.1 BBK 24.234-236 ISBN 978-5-7831-1896-8 © FSBEI HE «Ufa State Petroleum Technological University», 2020 © Raskil’dina G.Z., 2020 SIMPLE HYDROCARBONS The simplest hydrocarbons are those that contain only carbon and hydrogen. These simple hydrocarbons come in three varieties depending on the type of carbon- carbon bonds that occur in the molecule. As the name indicates, hydrocarbons are compounds composed of carbon and hydrogen. Those compounds whose carbon–carbon bonds are all single bonds are said to be saturated, because each carbon is bound to four atoms, the maximum number. Hydrocarbons containing carbon–carbon multiple bonds are described as being unsaturated, since the carbon atoms involved in a multiple bond can react with additional atoms, as shown by the addition of hydrogen to ethylene: Note that each carbon in ethylene is bonded to three atoms (one carbon and two hydrogens) but that each can bond to one additional atom if one bond of the carbon– carbon double bond is broken. Hydrocarbons сlassification Hydrocarbons and compounds derived from them generally fall into three large categories. Aliphatic hydrocarbons consist of chain of carbon atoms that do not involve cyclic structures. They are often referred to as open-chain or acyclic structures, e. g. propane, pentane, hexane. Alicyclic or simply cyclic hydrocarbons are composed of carbon atoms arranged in a ring or rings, e.g. cyclopropane, cyclopentane, cyclohexane. Aromatic hydrocarbons are a special group of cyclic compounds that usually have six-membered rings with alternative single and double bonds. They are classed separately from aliphatic and alicyclic hydrocarbons because of their characteristic physical and chemical properties, e. g. benzene, naphthalene. 3 Addition of hydrogen (hydrogenation) to a carbon-carbon double bond, reduces an alkene to an alkane. The process requires the presence of a metal catalyst, and for this reason, it is also called catalytic reduction. Catalytic reduction of alkenes is a very important reaction in the laboratory. In hydrogenation, both hydrogen atoms are added to the same side of the alkene molecule. The addition of water to an alkene is called hydration. In the presence of an acid catalyst, often 60% aqueous sulfuric acid, water adds to alkenes to produce alcohols. Hydrogen adds to the carbon of the double bond with the greater number of hydrogen; OH adds to alkenes in accordance with Markovnikov’s rule. Hydration of alkenes is a very important reaction both in the chemical industry and in biological systems. Hydrocarbons Aliphatic or open Cyclic or closed chain compounds chain compounds Saturated Unsaturated Alicyclic Aromatic alkanes (paraffins) C H n 2n+2 Alkadienes Alkenes Alkynes (Olefins) CnH2n (Dienes) CnH2n-2 C H n 2n-2 ALKANES Alkanes are the first class of simple hydrocarbons and contain only carbon- carbon single bonds. The alkanes are named by combining a prefix that describes the number of carbon atoms in the molecule with the root ending-ane. 4 The simplest member of the saturated hydrocarbons, which are also called the alkanes, is methane (CH ), which has a tetrahedral structure and can be described in 4 terms of a carbon atom using an sp3 hybrid set of orbitals to bond to the four hydrogen atoms (see fig.1). Fig. 1. The C‒H bonds in methane The next three members of the series are ethane (C H ), propane (C H ) and 2 6 3 8 butane (C H ), shown in fig. 2. Each carbon in ethane is surrounded by four atoms 4 10 and thus adopts a tetrahedral arrangement and sp3 hybridization, as predicted by the localized electron model. Alkanes in which the carbon atoms form long “strings” or chains are called normal, straight-chain, or unbranched hydrocarbons. As can be seen from fig. 2, the chains in normal alkanes are not really straight but zig-zag, since the tetrahedral C‒C‒C angle is 109.5°. ethane C H propane C H butane C H 2 6 3 8 4 10 Fig. 2. The molecular structures of ethane, propane and butane. Each angle shown in red is 109.5° 5 The normal alkanes can be represented by the structure where n is an integer. Note that each member is obtained from the previous one by inserting a methylene (CH ) group. We can condense the structural formulas by 2 omitting some of the C‒H bonds. For example, the general formula for normal alkanes shown above can be condensed to The first ten normal alkanes and some of their properties are listed in table 1. Note that all alkanes can be represented by the general formula C H . For example, n 2n+2 nonane, which has nine carbon atoms, is represented by C H , or C H . Also 9 (2+9)+2 9 20 note from table 1 that the melting points and boiling points increase as the molar masses increase, as we would expect. Table 1 Selected properties of the first ten normal alkanes The simple alkanes share many properties in common. All enter into combustion reactions with oxygen to produce carbon dioxide and water vapour. In other words, many alkanes are flammable. This makes them good fuels. For example, 6 methane is the principle component of natural gas, and butane is common lighter fluid: CH + 2O → CO + 2H O 4 2 2 2 ISOMERISM IN ALKANES Isomerism is the phenomenon when certain compounds, with the same molecular formula, exist in different forms owing to their different organizations of atoms. The concept of isomerism illustrates the fundamental importance of molecular structure and shape in organic chemistry. The molecular formula of organic compounds tells you how many atoms of each element are present in a molecule. The different structures lead to different properties. Two molecules that have the same molecular formula but differ in the way atoms are arranged are called isomers. The atoms are bonded together in a different order in each isomer. These are called structural isomers. The order of bonding in the isomer is the same; but the arrangement of atoms in space is different in each isomer. These are called stereoisomers. “Structural” isomers are widely called “conformational” isomers. The latter term is preferred in the IUPAC system of nomenclature. Structural isomerism occurs when two or more organic compounds have the same molecular formulae, but 7 different structures. These differences tend to give the molecules different chemical and physical properties. For example, butane can exist as a straight-chain molecule (normal butane, or n-butane) or with a branched-chain structure (called isobutane), as shown in fig. 3. Because of their different structures, these molecules exhibit different properties. For example, the boiling point of n-butane is ‒0.5°C, whereas that of isobutane is ‒12°C. Fig. 3. Normal butane (abbreviated n-butane) (a) and the branched isomer of butane (called isobutane) (b) Example 1. The isomers of pentane Pentane (C H ) has the following isomeric structures: 5 12 1. CH ‒CH ‒CH ‒CH ‒CH n-Pentane 3 2 2 2 3 2. Isopentane 3. Neopentane NOMENCLATURE Because there are literally millions of organic compounds, it would be impossible to remember common names for all of them. We must have a systematic method for naming them. The following rules are used in naming alkanes. 8 Rules for Naming Alkanes 1. The names of the alkanes beyond butane are obtained by adding the suffix -ane to the Greek root for the number of carbon atoms (pent- for five, hex- for six, and so on). For a branched hydrocarbon, the longest continuous chain of carbon atoms determines the root name for the hydrocarbon. For example, in the alkane the longest chain contains six carbon atoms, and this compound is named as a hexane. 2. When alkane groups appear as substituents, they are named by dropping the -ane and adding -yl. For example, ‒CH is obtained by removing a hydrogen from 3 methane and is called methyl, ‒C H is called ethyl, ‒C H is called propyl, and so on. 2 5 3 7 The compound above is therefore an ethylhexane (see table 2.). 3. The positions of substituent groups are specified by numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching. For example, the compound is called 3-methylhexane. Note that the top set of numbers is correct since the left end of the molecule is closest to the branching, and this gives the smallest number for the position of the substituent. Also, note that a hyphen is written between the number and the substituent name. 9