From Diamonds to Plastics: Carbon S Elemental Forms, Addition Polymers, and Substituted

Chapter 5 From Diamonds to Plastics: Carbon’s Elemental Forms, Addition Polymers, and Substituted Hydrocarbons

Review Questions

a) 6. CFCs, or chlorofluorocarbons, are molecules in which both chorine and fluorine are bonded to carbon atoms.

b)5. Carbon tetrachloride was used in fire extinguishers and in dry cleaning.

c) 4. Methylene chloride is a solvent used as paint thinner.

d) 3. Vinyl chloride is the starting material for PVC, or polyvinylchloride.

e) 2. TCE, or trichloroethene, is a solvent that was once used to extract caffeine from coffee.

f) 1. PCE, or perchloroethene, is a dry cleaning solvent in which all of the carbons are bonded to chlorine.

Two halogenated hydrocarbons that act as anesthetics are chloroform, CHCl3, and halothane, CF3CHBrCl.

CFCs are a class of compounds known as chlorofluorocarbons. They were used extensively as refrigerants in air conditioners, refrigerators, and freezers, and as propellants in spray cans. CFCs react with and destroy the protective ozone layer in the stratosphere.

A plastic is defined as a material that can be molded.

Unlike natural materials such as wood, plastics are more easily molded into shapes. Additionally, plastics don’t rot, rust, corrode, or break easily, and they can be permanently colored.

Polymers are substances that contain very long carbon-containing chains composed of a constantly repeating structural unit. Polyethylene is an example of a polymer.

Most plastics used today are synthetic polymers (produced in chemical laboratories and factories) that contain long carbon chains composed of repeating units called monomers.

Thermoplastics are plastics that melt, but do not decompose, upon heating. Thermoplastics can be repeatedly molded into various shapes when heated, and become hard when cooled.

Polyethylene is the simplest organic polymer. Ethylene is the starting material for this polymer.

10. HDPE, or high-density polyethylene, is denser than other forms of polyethylene because it is composed of long linear unbranched polymer chains that pack together very closely.

Monomers are the small molecules that serve as repeating units and combine to form long polymer chains.

Addition polymers are polymers that consist of intact molecules that combine together. Polyethylene is an example of an addition polymer composed of ethylene monomers.

a) The monomer unit is: -C-C-C-C-X-X-

b)The monomer unit is: -C=C-C-

c)The monomer unit is: -C=C-

Plasticizers are liquids that easily blend with polymers and act as lubricants between individual polymer chains. Plasticizers soften and provide flexibility to plastics.

Polymers such as PVC become brittle over time because plasticizers gradually leak out of plastics as they age. This lack of sufficient plasticizer results in brittle, cracking plastic material.

Fibers are composed of threadlike strands of solid material. Synthetic fibers are made when a polymer, either melted or dissolved in a liquid, is squeezed through a small hole in a device called a “spinneret.” These thin streams of highly viscous liquid solidify when cooled.

Foams are mixtures of two substances consisting of a gas trapped within another material. Styrofoam is a foam because it consists of a gas trapped within beads of polystyrene.

When the temperature of a polymer goes above its glass transition temperature, the polymer transitions from the glass state to the rubber state.

Straight chain polymers consist of molecules that are long continuous chains. Branched polymers are composed of molecules that have carbon chains or branches running off of the long continuous backbone chain.

Rubber is a polymer chain that contains carbon-carbon double bonds.

Latex is a liquid substance that oozes from rubber trees that consists of a mixture of small latex particles and water.

Vulcanization is a process in which sulfur chains of varying lengths react with the C=C bonds of rubber thereby cross-linking nearby polymer chains or cross-linking two parts of the same polymer chain.

Vulcanized rubber is harder, stronger, resists flowing, and is elastic because of the cross-linked polymer chains.

Elastomers are substances that are elastic. They can be stretched and they return to their original shape or position once the stress is released.

Branched polymers are composed of molecules that have carbon chains or branches running off of the long continuous backbone chain. The branched chains of these polymers are not cross-linked together. Cross-linked polymers have short chains of varying lengths that link or bind adjacent chains, or adjacent regions of the same chain, together.

The triangular symbol found on plastic products indicates that the material is recyclable. The number inside the triangle indicates the type of plastic used to make the container.

There are four ways to recycle plastics: a) reprocess the plastic by remelting or reshaping it, b) depolymerize the plastic back to its monomers so it can be repolymerized, c) transform it into a lower quality substance from which other materials can be made, and d) burn the plastic for its energy value.

Shortcomings associated with reprocessed plastic include the relatively high monetary and energy costs compared with the use of virgin plastic. Depolymerization requires the removal of small amounts of organic an inorganic additives in the original polymer. Additionally, processes that depolymerize are often expensive and typically produce a very low yield of the monomer. Transformation by “cracking” the polymeric molecules and producing synthetic crude oil or reacting the plastic with steam and oxygen gas to produce synthesis gas are expensive and the processes can release pollutants into the air. Finally, burning plastics often releases toxic chemicals and HCl gas.

In a diamond, all of the carbon atoms are bonded to four other carbon atoms by single C-C bonds. Thus, a diamond is a crystal composed of a network of carbon atoms. Because each of the C-C bonds is individually strong and the entire network is “welded” together as a unit, diamonds are extremely hard materials.

Diamonds are formed 150-200 kilometers below the Earth’s surface from carbon-containing material subjected to high temperatures and pressures, and are brought to the surface by the action of erupting volcanoes. Pure diamonds are colorless. Any color displayed by a diamond is the result of impurities trapped inside the crystal when it was formed (i.e., yellow color is due to an iron oxide impurity).

Diamonds are the hardest substance known, they are insoluble in water, oil, or any other solvent, they are poor electrical conductors, and they are good heat conductors.

A PAH is a polyaromatic hydrocarbon. Naphthalene is an example of a PAH.

PAHs are commonly produced as byproducts of incomplete combustion and enter the environment from gasoline and diesel engine exhaust, “tar” from cigarettes, and burning wood and coal. PAHs can also be found on the surface of charred or burnt food. PAHs, such as creosote found in treated wood, have leached into the water in some locations.

Many PAH pollutants are known or suspected human carcinogens. The most notable of these is benzo[a]pyrene, a molecule with five fused benzene rings.

Creosote is a coal tar derivative that has been used as a wood preservative.

36. Both graphite and diamond are composed of carbon atoms, but differ in bonding characteristics and structure. Diamond is composed of carbon atoms bonded to four other carbon atoms by single bonds, forming a very strong “fused” network of carbon atoms. Graphite is composed of carbon bonded to other carbons by both single and double bonds. As a result, graphite consists of large planes of carbon atoms that are weekly linked and can easily ”slide” over one another. The carbons within a plane are bonded to each other, but there are no covalent carbon bonds between the planes.

Composite materials are solid mixtures of nonmetallic materials.

38. Allotropes are different forms of a pure element. Three allotropes of carbon are diamond, graphite, and carbon black.

Soot is a form of carbon consisting of small crystals similar in structure to graphite, but containing about 10% hydrogen.

Activated carbon is a form of charcoal, an impure form of carbon produced by heating organic material in the absence of air, that has been cleaned of extraneous materials with steam. Because of its highly porous nature, activated charcoal is used to remove pollutants from vapors and liquids.

Carbon nanotubes are elemental forms of carbon having a hollow cylindrical structure. The surface of the cylinder is composed of mostly six-membered, fused rings, similar to those found in graphite sheets. The ends of the cylinder are closed because of the fusion of five- and six-membered rings to form a rounded non-planar surface to cap the molecule.

42. Carbon buckyballs are spherical forms of carbon. This “ball-shaped” molecule has rings of carbon atoms on its surface, and can be thought of as the fusion of the two caps of a nanotube.

Nanotechnology is the field of science and engineering that deals with the building of devices containing components having the dimensions of nanometers.

There are several problems associated with the use and recycling of tires. The quantity of tires discarded annually, about a third of a billion, along with the billions already stored in waste piles, makes this an enormous problem. Tires are made primarily from oil and are very flammable. Tire pile fires are quite common and release tremendous amounts of smoke, carbon monoxide, and toxins like PAHs. The use of old tires as a fuel source or as a filler for asphalt only consumes about 10% of the tires annually discarded. The high content of sulfur and PAHs make the disposal of this material a difficult and challenging problem.

Understanding Concepts

All of the structures of CH2Cl2 given on page 163 are identical because the four bonds to carbon form a tetrahedral arrangement. Thus, both C-H and both C-Cl bonds are identical. Additionally, since the molecules are always moving and tumbling in space, the three structures representing the arrangement of atoms in CH2Cl2 are superimposable on each other.

All three representations of chloroform are identical.

The three formulas are: CH2FCl, CHF2Cl, and CHFCl2.

a) As the ratio of halogen to carbon atoms in a molecule increases, the boiling point of the molecule also increases.

b) As the ratio of halogen to carbon atoms in a molecule increases, the molecules go from a gaseous state to a liquid state.

–CH2-CCl2-CH2-CCl2-CH2-CCl2-CH2-CCl2-CH2-CCl2-CH2-CCl2 -.

Anesthetics dissolve in cell membranes and block nerve impulses from reaching the brain.

The repeating unit of this polymer is -CCl2-CHCl-. The monomer that can be polymerized by an addition process to obtain this polymer is CCl2=CHCl.

Long chain alkanes and HDPE are similar in structure as they both contain long segments or chains of carbon atoms. In contrast to alkanes, which typically have relatively small numbers of carbons, the number of carbons in a chain of HDPE is on the order of 20 thousand. In addition, the number of carbon atoms in a long chain alkane is constant, whereas different polymer chains in the same sample of polymeric material vary slightly in their length and mass. While both materials have similar properties, such as a waxy, opaque appearance, there are some striking differences. HDPE possesses considerable structural strength, rigidity, and toughness not exhibited by the long chain alkanes.

Polymers are generally more flexible in their rubber state because of the presence of liquid-like random regions within the molecule that provide little resistance to the distortion of their shape.

Polystyrene is a thermoplastic that can be readily molded into various shapes. It is a good choice for use in insulation because small beads of polystyrene can be impregnated with a small amount of a volatile liquid and heated to produce a foam without decomposing.

All plastics are polymers, but all polymers are not plastics. For example, both the proteins in muscles and the genetic material in living cells are polymers of smaller biological molecules. While classified as polymers, these materials are not plastics.

The properties desired in a polymer used to store food are both flexibility and a resistance to penetration by oxygen.

High-density polymers are composed of unbranched chains and pack tightly together to form solids that are relatively high in density. Low-density polymers consist of branched chains that do not pack as tightly in the solid state.

Yes, the structures of natural and synthetic rubber differ. Rubber has the following structure:

In natural rubber, X is the methyl group (-CH3). In synthetic rubber materials, the X group varies. The X group is hydrogen in polybutadiene rubber and the X group is chlorine in neoprene.

Polymers containing alternating single and double bonds can be altered to conduct electricity. These extended networks of carbon atoms, each of which forms a double bond, behave like metals. Due to their limited length, however, they can not form “wires” of considerable length. Therefore, in order for the electric current to flow from one polymer chain to the next, a small amount of material that assists in the transfer of electric current between the polymer chains in a solid is added. When altered in this fashion, these polymers are converted into conductors in which the current passes from one end to the other.

60. Desirable properties of polymers to be recycled include the lack of inorganic and organic additives and the ability to burn cleanly. Ideally, the combustion of polymeric material should not result in the production of toxic organic compounds or significant amounts of hydrogen chloride gas.

Graphite is a form of carbon that consists of sheets of fused six-carbon benzene-like rings that are stacked one upon another. Carbon nanotubes are composed of a sheet of similarly fused six-carbon networks shaped as a cylinder.

62. In the structure of a diamond, all of the carbon atoms are bonded to four others to form an extended network of atoms. Naphthalene, however, consists of carbon atoms with alternating single and double bonds that form two fused rings. Unlike the structure of a diamond, each of the carbon atoms, except those on the fused face, are bonded to a single hydrogen atom. These differences impart characteristic properties on each of the materials. Diamonds are extremely stable, “hard” materials that are non-volatile and are insoluble in water, oil, or other solvents. In addition, diamonds are extremely unreactive. Naphthalene, however, is a solid compound with a melting point of 90oC. It is quite volatile, soluble in organic solvents, and is chemically reactive.

Synthesizing Ideas

63.

POLYMER / MONOMER / PROPERTIES
HDPE / Ethene / Hard, waxy, opaque, structural strength, toughness, and rigidity.
PVC / Vinyl chloride / Rigid and strong. Can be made flexible by the addition of plasticizers.
POLYPROPYLENE / Propene / Hard, opaque, structural strength, stronger, more rigid, and can withstand higher temperatures than HDPE. Can be drawn into fibers.
POLYSTYRENE / Styrene / Transparent, hard, brittle, thermoplastic, can be molded into different shapes. Lack of frictional resistance to motion, repels water and “breathes.”
PFTE / Tetrafluoro-ethylene / Very high resistance to chemical attack and thermal decomposition
SYRAN WRAP / Vinylidine chloride and vinyl chloride / Flexible and impermeable to oxygen

64. a) Teflon is highly resistant to chemical attack and thermal decomposition. It also exhibits minimal frictional resistance and is impermeable to water.

b)Polystyrene is ideal for CD cases because it is transparent, hard, brittle, and can be molded into different shapes.

c)PVC is rigid and strong making it the ideal material to replace metal pipes. It can also be made flexible and strong by the addition of plasticizers.

Carbon nanotubes are elemental forms of carbon having a hollow cylindrical structure. The surface of the cylinder is composed of mostly six-membered, fused rings, similar to those found in graphite sheets. The ends of the cylinder are closed because of the fusion of five- and six-membered rings to form a rounded non-planar surface to cap the molecule. Carbon buckyballs are spherical forms of carbon. This “ball-shaped” molecule has rings of carbon atoms on its surface, and can be thought of as the fusion of the two caps of a nanotube. Possible uses for nanotubes include hydrogen storage, chemical detection, and muscle fibers. They may also find use as wires, semiconductors, superconductors, and surgical devices. Buckyballs have potential utility as transistors and superconductors and are able to encapsulate small atoms.

66.

a) The most common polymer used in medical devices is PVC.

b) Essential properties of plastics used for medical devices include clarity, transparency, flexibility, sterilizability, ease of processing, low cost, compatibility with other medical products, and resistance to chemical stress cracking.

c) There has been concern expressed about the use of phthalate esters as plasticizers in vinyl medical products. While phthalates, when fed to mice and rats caused cancer, similar studies using monkeys have not shown a link between phthalate esters and cancer.

d)Unfortunately, alternatives are not readily available. Currently, there are no commercially available substitutes for PVC for the storage of red blood cells.

a) The properties of buckyballs that make them good candidates for use in drug delivery include their stability, numerous attachment points, the ability to be readily absorbed into the bloodstream, and the ability to cross the blood-brain barrier.

b)Benzene-based therapeutic and/or diagnostic agents would be linked to sixty carbon sites inside the structure, and the entire material injected, ingested, or placed into the body.

There are several advantages of using buckyballs for drug deliver systems. These include their stability, their ability to be readily absorbed into the bloodstream, their ability to cross the blood-brain barrier, and their ability to specifically target an organ system. All of these properties help to increase the bioavailability of the drugs relative to the current modalities of pills and injections.