Properties of Organic Compounds & Crude Oil Refining

Section 9.5 and 9.6 (pg. 386-400)

Properties of Organic

Compounds & Crude Oil

Refining Today’s Objectives:

1) Compare boiling points and solubility of organic compounds

2) Describe fractional distillation and solvent extraction

3) Describe major reactions for producing energy and economically important

compounds from fossil fuels

Physical Properties of Simple Hydrocarbons

Alkanes Non-polar molecules

Only intermolecular forces are London Force

Boiling point and melting point increase with number of carbons

All insoluble in water (like dissolves like) – nonpolar and polar don’t mix

1-4Cs = gas, 5-16Cs = liquid 17 and up = solid at SATP

Alkenes Non-polar molecules, therefore insoluble in water

Boiling points slightly lower than alkanes with the same number of carbons

due to less electrons (unsaturated), resulting in lower London Forces

Alkynes Non-polar molecules, therefore insoluble in water

Higher boiling points than alkanes and alkenes with similar C #s

Accepted explanation: Linear structure around triple bond allows electrons to

come closer together than in alkanes/enes, resulting in greater London Force

Branching The more branching, the less significant the London Force (~lower b.p.)

- more surface area in straight chain hydrocarbons allows more

separation of charge, resulting in greater London Force

- see Table #3 pg. 378 (i.e. pentane (with 5Cs) has a b.p. of 36oC

which is much higher than dimethylpropane (5Cs) -12oC) = because

branching decreased the strength of the London force

Physical Properties of Hydrocarbon Derivatives

Alcohols Much higher boiling points than hydrocarbons (1-12Cs are liquids at SATP)

due to hydrogen bonding between hydroxyl groups of adjacent molecules

Small alcohols are totally miscible in water, but the larger the hydrocarbon

part of the alcohol (nonpolar part), the more nonpolar the alcohol is

Carboxylic

Acids

Like alcohols they have hydrogen bonding, but is more significant due to the

C=O. This means greater bps and solubility than alcohols with same number

of Cs.

Carboxylic acids with 1-4Cs are

completely miscible in water

Esters Fruity odour in some cases

Polar but they lack the –OH bond therefore do not have hydrogen bonding, so

lower bps than both alcohols and carboxylic acids

Esters with few carbons are polar enough to be soluble in water

Compound Boiling Point (oC)

butane -0.5

butan-1-ol 117.2

butanoic acid 165.5

Summary Table - Organic

In your homework book (pg. 7), there is a summary table

of all of the organic compounds we have studied. This

will be a good page to reference when studying

Sample Question

Predict the relative order of boiling points of the following

compounds (lowest to highest). Explain your reasoning.

butanol but-1-ene cyclobutane butanoic acid butane

Lowest -------------------------------------------------------------> Highest

but-1-ene butane cyclobutane butanol butanoic acid

Reasoning: but-1-ene has lower LF’s for than butane because it is

unsaturated, cyclobutane has an additional bond because cyclic,

butanol has H-bonding, butanoic acid has stronger H-bonding)

Which would be soluble in water?

Butanol and butanoic acid – because they are the only polar molecules

and like dissolves like!

Crude Oil Refining

Crude oil is a complex mixture of hundreds of thousands

of compounds, all of which have different boiling points

We can take advantage of these different b.p.’s and

physically separate the different components using heat

This process is called fractional distillation or fractionation

A fractional distillation tower

contains trays positioned at

various levels.

Heated crude oil enters near

the bottom of the tower.

The bottom is kept hot, and the

temperature gradually

decreases toward the top of

the tower.

As compounds cool to their

boiling point, they condense in

the cooler trays. The streams of

liquid (called fractions) are

withdrawn from the tower at

various heights along the tower.

Electronic Visual

A more detailed look…

The vaporized components of the

crude oil rise and gradually cool.

To get from one level to the next, the

vapours are forced to bubble through

the liquid condensed in each tray.

The figure shows the bubble caps used

to allow this to happen.

If a gas cools to its boiling point, it will

condense and be piped out through

the draining tube

Q: How does the number of carbon atoms in a hydrocarbon chain

affect its boiling point?

Smaller molecules have fewer electrons, so weaker London forces

compared with larger molecules. The fractions with higher boiling points

are found to contain much larger molecules (see Table 1 pg. 387)

Crude oil is heated in the

fractionation tower without air being

present to reduce the risk of mixtures

starting to burn or explode

Cracking

Cracking: large hydrocarbons are broken into smaller fragments

Historically, thermal cracking used extremely high temperatures but

created large quantities of solid coke.

Now, catalytic cracking uses a catalyst to speed up the reaction and

produce less residual products like tar, asphalt and coke

Example: C17H36(l) C9H20(l) + C8H16(l) + C(s)

larger molecules smaller molecules + carbon

In 1960, hydrocracking was developed, which combines catalytic

cracking and hydrogenation and produces no coke.

Example: C17H36(l) + H2(g) C9H20(l) + C8H16(l)

larger molecule + hydrogen smaller molecules

Oil Refining

The refining of crude oil can be divided into two main categories:

1. Physical Processes

Fractional Distillation: see previous slides

Solvent Extraction: solvent is added to selectively dissolve and

remove an impurity or to separate a useful product from a

mixture

2. Chemical Processes

Cracking – larger molecules are broken down into smaller ones

Reforming – large molecules are formed from smaller ones

These chemical processes are needed because fractional distillation

does not produce enough of the hydrocarbons that are in demand

(i.e. gasoline) and produces too much of the heavier fractions

Catalytic Reforming and Alkylation

Catalytic Reforming: improves the quality of the gasoline

aliphatic molecule aromatic molecule + hydrogen

Alkylation: increases the branching; improves the quality of the fuel

aliphatic molecule more branched molecule

(AKA: isomerization because it converts molecules into a branched isomer)

FYI pg. 392 on

Octane Numbers

Combustion Reactions

Burning of hydrocarbons in the presence of oxygen

Complete Combustion: abundant supply of oxygen;

products are carbon dioxide, water vapour and heat

Ex. C3H8(l) + 5O2(g) 3CO2(g) + 4H2O(g)

Incomplete Combustion: limited supply of oxygen; products

are carbon monoxide, soot (pure carbon) or any

combination of carbon dioxide, carbon monoxide and soot

in addition to water vapour and heat

Ex. 2C8H18(l) + 17O2(g) 16CO(g) + 18H2O(g)

OR 2C8H18(l) + 9O2(g) 16C(s) + 18H2O(g)

** Assume complete combustion unless specified otherwise

Balancing FYI

Ex. 2C8H18(l) + 17O2(g) 16CO(g) + 18H2O(g)

Can also be balanced using a fraction (you need to be

comfortable using this method) – divide each number by 2

C8H18(l) + 17/2 O2(g) 8CO(g) + 9H2O(g)

Ex. 2C8H18(l) + 9O2(g) 16C(s) + 18H2O(g)

can also be balanced as …

C8H18(l) + 9/2 O2(g) 8C(s) + 9H2O(g)

Today’s homework

Read pages 410-416

Pg. 388 #2

Pg. 391 #11

Pg. 397 #4 b, c, d only

Pg. 430 #11

What is coming up tomorrow?

Hydrocarbon Quiz #3 (all organic compounds)

Use Homework Book pg. 8 as practice quiz