of intermediates and conjunct poly­mers in the complicated alkylation process. Red oil now is clearly known to enter into various reactions and, in some cases, leads to trimethylpentanes, says Dr. Eckert.

Red oil contains some of the com­plicated ions which are important in the mechanism proposed by the Pur­due group. These ions include tertiary (or secondary) cations, which form from a proton added to double bonds; allylic cations, which form because of conjugated double bond structures of the red oil; and protons present in the acid phase. Numerous reactions occur between the ions and olefins to form large red oil cations, often tertiary, but sometimes secondary. These cations react reversibly with isobutane to form tert-buty\ ions. At the same time, some of the large red oil ions decom­pose to release isobutylene, which re­acts with tert-butyl ions to make tri-methylpentyl cations. These cations isomerize and add a hydride ion to form trimethylpentanes.

A second sequence of reactions to form trimethylpentanes occurs, as has been postulated in the past, out this sequence is of less importance than the first. The tert-butyl cation in the acid phase reacts with isobutylene and 2-butene as the latter transfers from the hydrocarbon phase to the acid phase. A trimethylpentyl cation forms which isomerizes and picks up a hydride ion to form a trimethylpentane.

In a third and still less important sequence, trimethylpentanes form pri­marily from olefins and red oil.

Self-alkylation. A fourth sequence —self-alkylation of isobutane—is of most relative importance when isobu­tane is alkylated with propylene or C5

olefins. In this sequence, the acid and red oil dehydrogenate part of the iso­butane to isobutylene,, which reacts with tert-butyl ions as before to form trimethylpentanes.

The Purdue group has analyzed available results for alkylations cata­lyzed by hydrogen fluoride. The limited data indicate that HF alkylate differs from sulfuric acid alkylate. For example, H F alkylates obtained when isobutylene is used as the olefin con­tain more trimethylpentanes, especially 2,2,4-trimethylpentane, but less light ends; and when 1-butene is used, H F alkylates have much higher amounts of dimethylhexanes, especially 2,3-dimethylhexane.

Certain features of the alkylation mechanism still need verification and added details, Dr. Albright says. For example, more work is needed on the chemistry of the acid phase, especially that of the organic materials dissolved in the acid phase. More HF alkylation studies also are needed to further com­pare the two types.

SAFE. Charles A. Farish, executive director of the National Sanitation Foundation, says that plastic pipe will not affect the appearance, taste, or odor of drinking water

Plastic pipe is safe for drinking water

W A T E R , A I R & W A S T E

Plastic pipe is safe and will not affect the appearance, taste, or odor of drinking water, according to Charles A. Farish, executive director of the National Sanitation Foundation (NSF). Mr. Farish does have some reserva­tions about the chemicals used to sta­bilize plastic pipe, however.

Lead compounds, he says, should not be used. While this warning isn't necessary in the U.S., since lead sta­bilizers are not used in plastic pipe for potable water here, it does have im­plications for Europe, where lead-sta­bilized plastic pipe has been used ex­tensively.

Mr. Farish told the Forum on Environmental Quality (Water) held jointly with the Divisions of Analyti­cal and Industrial and Engineering Chemistry that a series of tests per­formed by NSF on lead-stabilized plas­tic pipe show that total soluble lead extracted from samples exceeds the maximum limit for lead in drinking water established by the Public Health Service. Although the comparative study is continuing, "the data acquired to date do not support the use of lead-stabilized plastic pipe for transporting potable water," he explains.

NSF, a nonprofit, nonofRcial agency for research, education, and service in areas concerned with man's health and environment, now author­izes 220 plastic producers and fabrica­tors to use its seal. The seal indicates that the plastic pipe is nontoxic, will not adversely affect the appearance,

taste, or odor of water, and conforms to applicable physical standards under which it is produced and identified.

Five types. Plastic pipe was first introduced in Europe in 1930 and in the U.S. in 1940. Five major types of thermoplastics are used in manu­facturing the pipe in the U.S.: acrylo-nitrile-butadiene-styrene (ABS), poly­ethylene (PE) , polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), and polybutylene (PB).

In recent years, plastic pipe has as­sumed a major role in potable water transportation. More than 200,000 miles of plastic pipe and fittings are now in domestic service. Among its numerous advantages are light weight, high strength, economical installation, and excellent corrosion resistance.

While lead, cadmium, strontium, lithium, and antimony can be used in plastics formulations as stabilizers, lead and cadmium are particularly hazard­ous, Mr. Farish points out. All soluble lead salts are toxic. Even small concentrations of lead continuously present in drinking water may cause serious illness or death. Lead poison­ing is not normally a problem in hard water since lead carbonate and sulfate are insoluble. Lead is a cumulative poison because elimination, which is through the kidneys, is very slow.

Cadmium accumulates in the soft tissues of the body, resulting in anemia, poor metabolism, arterial changes in the liver, and, at high concentrations, death. Acceptable upper limits for lead and cadmium in drinking water are 0.05 and 0.01 mg. per liter, re­spectively, according to drinking water standards published by the Public Health Service.

SEPT. 15, 1969 C&EN 57