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COMMON SOURCES AND USES OF ALKANESThe main source of hydrocarbons is petroleum.

Petroleum refining processes are involved in separation, purification and increasing the yield of the wanted components of crude petroleum.

Fractional Distillation is the process of separating a number of components (fractions) of a liquid mixture using the fact that each component will have a different boiling point.It is used in the petroleum industry for separating crude petroleum into a number of fractions, each containing a large number of compounds with different boiling point

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Modern Fractionation Tower

Crude petroleum is heated to about 400oC and the vapours pass into the tower. As the vapours pass through the openings in the trays they condense to the liquid phase. The more volatile portions of the liquid re­vaporize and rise to the next tray. Thus various components of crude separate themselves.

A C1 ­ C5 gaseous fuel for heating homesBC5 ­ C12 motor gasolineCC12 ­ C16 kerosene; fuel for diesel and jet enginesDC15 ­ C18 heating oil for furnacesEC16 ­ C20 lubricating oilFC20 ­ C25 paraffin waxG C26 ­ up asphalt and tars

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Combustion ReactionsHydrocarbons in the range of 7­12 carbons per molecule are the most sought after fractions in crude oil because they eventually become gasoline. Other hydrocarbons such as kerosene or jet fuel (C14H30) and diesel (C16H34) are also valuable products of refining because like gasoline they are fuels used in transportation. The most common reaction that these hydrocarbons undergo is combustion.When sufficient amounts of oxygen are available, the combustion of hydrocarbons is complete resulting in the production of carbon dioxide and water vapor. The general form of the equation is:a hydrocarbon + oxygen gas carbon dioxide + water vapourexample:

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Incomplete Combustion CxHy + O2(g) → CO2(g) + C(s) + CO(g) + H2O(g)

Ex:

About 90% of the crude oil that enters a refinery exits as gasoline, furnace oil, and jet fuel. The other 10% or so is converted to hydrocarbons like ethene and styrene ­ starting materials used in the plastics industry.

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Cracking produces compounds essential to the plastics and fuels industries. The short chain alkenes are raw materials in the plastics industry. Longer chain alkenes are used to produce the very valuable branched alkanes that give gasoline a higher octane rating.

Since certain hydrocarbons are in greater demand than others, oil refineries use special processes to convert less valuable hydrocarbons into more valuable ones. Two of the most important processes used for this purpose are cracking and reforming.

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Cracking (Thermal or Catalytic): a process used in the petroleum industry to break down long chain alkanes into smaller more useful chains. C12 and up are used as cracking stock.

CRACKING

1) There is no way to predict the size and type of hydrocarbon.2) The process often requires hydrogen as a reactant.

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Thermal Cracking: cracking of a hydrocarbon using heat

Catalytic Cracking: cracking of a hydrocarbon using a catalyst

Catalyst: a substance, which helps a chemical reaction, occurs without being used up.Examples:a) The cracking of heptane into propane and butane.

­C­C­C­C­C­C­C­ + H2 ­­­> ­C­C­C­ + ­C­C­C­C­

b) The cracking of 2­methylpentane to produce propane. CH3

|­C­C­C­C­C­ + H2 ­­­> ­C­C­C­ + ­C­C­C­

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c) The cracking of 1­butene to produce ethyne and ethane.

­C­C­C=C­ ­­­­­­> ­C=C­ + ­C­C­

(don't need to add hydrogen, 2H are removed when the triple bond forms)

d) The cracking of a hydrocarbon, which produces methane and propane.

­C­C­C­C­ + H2 ­­­­> ­C­ + ­C­C­C­

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REFORMING

Reforming (Thermal or Catalytic) : a process used in the petroleum industry to convert straight chain alkanes into branched alkanes having a high octane rating.Thermal Reforming:Reforming of a hydrocarbon using heat

Catalytic Reforming: Reforming of a hydrocarbon using a catalyst

1) two small hydrocarbons make a larger one.2) process often produces hydrogen

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Examples: Draw structural diagrams for all organic reactants and products.

a) Ethane reacts with 2­butene to produce 3­methylpentane

­C­C­ + ­C­C=C­C­ ­­­­> ­C­C­C­C­C­ | CH3

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b) Octane is produced from the reaction of hexane and ethane.

­C­C­C­C­C­C­ + ­C­C­ ­­­> ­C­C­C­C­C­C­C­C­ + H2

c) 2­methylbutane and propane react to form octane. CH3 |­C­C­C­C­ + ­C­C­C­ ­­­­> ­C­C­C­C­C­C­ + H 2

| | CH3 CH3

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PolymerA polymer is a huge molecule that is formed when hundreds or thousands of small molecules called monomers are bonded together.

Polymers are literally everywhere. Natural Polymers originate in living things. Examples are cotton, wool, carbohydrates, proteins, DNA and lipids.The plastic around the screen you are viewing and the plastic that makes up the mouse you are holding is polystyrene­ a synthetic polymer.

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Representing Organic Structures

Polymers

Click on the pictures for the chemical names for each polymer and a structural example.

Polyethylene terephthalate High­density polyethylene

Polyvinyl chloride Low­density polyethylene

HDPE=High­density polyethylenePETE=Polyethylene terephthalate

LDPE=Low­density polyethylenePVC=Polyvinyl chloride

Plastics that we know and love (and can recycle) are organic polymers.

Polymers are large molecules composed of repeating structural units, or monomers, typically connected by covalent chemical bonds. These may be single straight chains, or can be branched. In addition to plastics, several important biomolecules are also polymers, such as DNA and cellulose.

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Synthetic polymers are things like Dacron, Teflon, nylon, polyvinyl chloride (PVC), polyethylene, polypropylene and polystyrene. Just think of it ­ no plastic bags, pipes or containers, no modern carpeting, no high­tech polishes and waxes ­ the list is extensive. About half of all synthetic polymers are the products of addition polymerization reactions. Natural polymers and the remainder of the synthetic polymers are formed by condensation polymerization.

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Addition Polymerization :is when molecules of the same type of monomer(unsaturated hydrocarbon) are joined together under specific conditions to form one very long molecule (the polymer). .

About half of all synthetic textile fibres are produced by addition polymerization. highest temperature n CH2 = CH2 ­­­­­­­­­­­­­­­> (­ CH2 ­ CH2 ­)n high pressure ethylene polyethylene (plastics) monomer polymer

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Ex 1: Polyvinyl chloride, plastic is the product of the additionpolymerization of chloroethene

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Ex 2: The addition polymerization of 1,1,2,2­tetrafluoroethene will produce Teflon.

polytetrafluoroethylene (Teflon­non­stick cooking)

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Ex 3: Polymerization of propene (propylene)

Polypropylene (fishing nets)

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Additional Questions

Short Answer

Given a section of the polymer Neoprene below, circle three monomer units.

CH2=C­CH=CH2

Cl

­CH2­C=CH­CH2­CH2­C=CH­CH2­CH2­C=CH­CH2­CH2­C=CH­CH2­CH2­C=CH­CH2­

Cl Cl Cl Cl Cl

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Condensation Polymerization Condensation Polymerization: involves joining monomers together into a larger molecule called a polymer.

+ 2n H2O

+ 2n H2O

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Esters and amides are produced by condensation reactions. A condensation polymer is the product of condensation chain reaction. With each monomer that becomes part of the polymer, a by­product molecule is produced. Unlike addition polymers, which can only grow at one end, a condensation polymer can grow in two or more directions at once. Here are some examples of molecules involved in condensation polymerization reactions:

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Here are some examples of molecules involved in condensation polymerization reactions:

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What do these molecules have in common? two active sitesHow do they differ from molecules that undergo addition polymerization?

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