Organometallic Compounds in the Environment / Edition 2

Organometallic Compounds in the Environment / Edition 2

ISBN-10:
0471899933
ISBN-13:
9780471899938
Pub. Date:
06/09/2003
Publisher:
Wiley

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Overview

Organometallic Compounds in the Environment / Edition 2

A knowledge of the chemical structure and concentration oforganometal compounds throughout the ecosystem is important inworking out the pathways and mechanisms by which metals distributethemselves throughout the environment. Treating the topic as anintegrated subject area, the Second Edition of OrganometallicCompounds in the Environment covers all the recent developmentsin analytical techniques and reports all the new work that has beenachieved since the first book.

  • Covers the general importance and characteristics oforganometallic species.
  • Includes general developments in analytical techniques.
  • Discusses several minority elements including antimony andselenium.

The book addresses the subject in a single, manageable size andeach chapter can be used either as a single review or sequentiallywithin the topic area.  A useful resource for all researchersand scientists in industry working with organometallic compounds,including, chemists, environmentalists and ecologists.

 

Product Details

ISBN-13: 9780471899938
Publisher: Wiley
Publication date: 06/09/2003
Edition description: REV
Pages: 434
Product dimensions: 6.16(w) x 9.29(h) x 1.21(d)

About the Author

Professor Peter Craig is an Emeritus Professor in the School of Molecular Sciences at De Montfort University, Leicester, UK. His research has been particularly concerned with metal methylation, reactions and transport in the environment and with the roles of mercury, tin, lead, arsenic and antimony in the natural environment.

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Organometallic Compounds in the Environment


John Wiley & Sons

Copyright © 2003 John Wiley & Sons Ltd
All right reserved.

ISBN: 0-471-89993-3


Chapter One

Occurrence and Pathways of Organometallic Compounds in the Environment-General Considerations

P.J. CRAIG School of Molecular Sciences, De Montfort University, Leicester, UK

GEORGE ENG Department of Chemistry, University of the District of Columbia, Washington, DC, USA

and

R.O. JENKINS School of Molecular Sciences, De Montfort University, Leicester, UK

1.1 SCOPE OF THIS WORK

The compounds considered in this work are those having metal-carbon (normally metal-alkyl) bonds, and which have environmental implications or properties. There is limited reference to metal-carbon [pi] systems (e.g. Mo[(CO).sub.6], W[(CO).sub.6]([eta]-C[H.sub.3][C.sub.5][H.sub.4]Mn[(CO).sub.3]) and mechanistic discussion of metal hydrides and ethene (e.g. decomposition by ß elimination). In terms of formation of organometallics, methyl groups predominate but there is also reference to other metal hydrocarbon compounds (e.g. ethyl or phenyl mercury, ethyl leads, butyl tins). However, much of this work refers to metal methyl compounds as these are formed naturally in the environment (biomethylation)

The thrust of the work involves a good deal of analytical chemistry, but that is not the prime focus of the book. However, without the modern developments inanalytical chemistry of the past 50 years, knowledge of most of the chemistry described in this book would barely exist. The analytical work that has led to this chemistry is described in the appropriate chapter but it is not the main theme. Several recent and comprehensive works that focus on the analytical chemistry of the environment have recently appeared and the reader is referred to those for the technical details of the analytical chemistry (see Standard Reference Sources and References at the end of the book).

Amongst these, the recent comprehensive work by Crompton [1] focuses almost exclusively on the analysis of metal cations with minor consideration of organometallic compounds, and as its title denotes, is concerned with analysis from aqueous media. Similarly the work of Ure and Davidson [2] is mainly directed towards metal cations. The recent work edited by Ebdon et al. [3] also focuses more on analytical chemistry but takes full account of the complete molecular identity of the metallic compounds present (not focusing exclusively on organometallic compounds), i.e., speciation. (The importance of speciation is discussed later.)

Given that the stability, transport and toxicities of organometallic compounds depends on the number and type of the metal alkyl or aryl groups present, and that different compounds of the same or different metals may coexist at the same location in the environment, then separate detection of each species (speciation) is necessary. Separation and detection go together in so-called interfaced or hyphenated analytical systems. This is of particular importance because such species, although having real environmental and/or toxicity effects, often occur at very low concentrations in the environment (ppb, ppm-see later for definitions).

Nevertheless a broad statement on analysis needs to be made. There are two considerations:

(i) The metal, organometallic fragment or full compound needs to be detected by a sufficiently sensitive method (e.g. Hg, C[H.sub.3][Hg.sup.+], C[H.sub.3]HgCl respectively), and

(ii) as a variety of organometallic compounds of the same element may be present together in the same matrix (e.g. butyltins, butyl/methyltins) and they each have different toxicity and environmental properties, then they must be separated before individual detection.

The main methods of detection are as follows: (i) Atomic absorption spectroscopy (flame, graphite furnace, Zeeman, hydride generation/quartz furnace),

(ii) atomic fluorescence spectroscopy (alone or via hydride generation),

(iii) atomic emission spectroscopy (usually inductively coupled plasma),

(iv) voltammetry,

(v) mass spectrometry (conventional or chemical ionization, electrospray, tandem, isotope dilution, plasma),

(vi) X-ray and neutron methods.

The main methods of separation are:

(i) Gas chromatography (conventional or capillary),

(ii) thermal desorption methods (which depend on boiling points),

(iii) high performance liquid chromatography,

(iv) flow injection methods,

(v) ion exchange chromatography,

(vi) ion chromatography.

Many organometallic compounds, or cations are insufficiently volatile to undergo gas chromatography, but may be induced to do so by derivatization.

This is generally achieved by (formally) S[N.sub.2] attack by hydride (from NaB[H.sub.4]), ethyl (NaB[([C.sub.2][H.sub.5]).sub.4]) or other alkyl group (e.g. from a Grignard reagent), e.g. Equation (1.1)

(1.1) [Mathematical Expression Not Reproducible In ASCII] X = environmental counter ion (in this case not riboside-see Chapter 5)

This has been widely achieved, even in the case of mercury where it had been thought that mercury hydrides were too unstable for use in analysis.

Coupling of these separation and detection techniques is now ubiquitous and provides an intensive battery of techniques for analytical work, well described in Reference. Without these, little knowledge of organometallic compounds in the environment would be possible.

The present work is also not primarily a work of toxicology although the toxicity properties of the compounds are discussed in the chapters element by element. The reader is referred to several excellent works specifically dedicated to toxicity studies of organometallic compounds.

The present work is a consideration of the inputs (natural and anthropogenic) and/or formation of organometallic compounds in the natural environment (sediment, water and atmosphere), their properties and behaviour there, and their ultimate fate. Although much of our understanding in this field is derived from analytical chemistry and the methods are described where needed, the theme of the work is the overall behaviour of organometallics in the environment, not their analysis. Compounds are covered by chapters on an element-by-element basis.

Organometallic species (i.e. compounds, complexes or ions) may be found in the natural environment either because they are formed there or because they are introduced there. To date, the behaviour of the latter group is better understood, and their environmental impact has been assessed by studies of their direct toxicities, their stabilities and routes to decay, and by toxicity studies of their decay products. Organometallic compounds entering the environment may be deliberately introduced as products whose properties relate to the environment (e.g. biocides) or they may enter peripherally to a separate, main function (e.g. gasoline additives, polymer stabilizers). Compounds of arsenic, mercury, tin and lead have important uses as organometallic compounds. Their role and behaviour in the environment are covered in the appropriate chapters of this work (Chapters 2 to 5). The behaviour of other organometallic species in the natural environment is also covered (Chapters 6 to 10). However, not all organometallics found in the environment are introduced-some are formed after entry as inorganic species and constitute the organometallic components of global biogeochemical cycles. This process of environmental methylation is usually termed biomethylation and is, as the name implies, almost exclusively concerned with formation of metal-methyl bonds (although ethyl mercury has been found in the environment in circumstances removed from likely input as a product). Recent work has demonstrated the occurrence of transition metal carbonyls, likely to have been formed in the environment (see below).

1.2 GENERAL APPROACH: SPECIATION, CONCENTRATIONS AND TERMINOLOGY

This work considers those organometallic compounds that have relevance to the natural environment. It is concerned with compounds that are found there, or which may be formed there, or which may react or be transported within the environment. Accordingly we discuss inputs, formation, transportation and decay. The approach is to consider these processes element by element in each chapter. The present chapter links the work by considering those fundamental aspects of organometallic chemistry that are relevant to the environmental chemistry of the elements discussed in each chapter, including stabilities, and mechanisms of environmental formation and decay.

It is at this point that further consideration of the term 'speciation' should be made. A generation ago, and indeed much legislation concerning pollution, etc. still occurs in this context, chemists had to be content with discussing a contaminant by its defining element (e.g. total arsenic, mercury concentrations, etc.). In parallel with many chemists becoming environmental chemists, technology and necessity prompted further identification into partial or complete molecular identification of the contaminant (e.g. methylmercury, C[H.sub.3][Hg.sup.+], arsenobetaine, ([C[H.sub.3]).sup.+.sub.3]AsC[H.sub.2]CO[O.sup.-]). Such full operational identification of a compound within a larger matrix is now commonly termed 'speciation'. Where possible, to accord with a speciation approach, we will discuss the chemistry in terms of compounds.

Additionally of course, speciation is now not only more possible, it is essential. The main toxicity and environmental properties depend markedly on what compound is present, not on what metal. Some arsenic compounds are notoriously toxic (e.g. [As.sub.2][O.sub.3]), but some are effectively non-toxic (e.g. arsenobetaine). Toxicity also depends on the degree of alkyl substitution of a metal and the identity of the organic (alkyl) group, and it varies also for the same compound towards different (biological) species. Residence times may also vary with species (e.g. C[H.sub.3][Hg.sup.+] (long) and [Hg.sup.2+] (shorter) in biological tissue), and this can determine toxic impact. In addition to toxicity, transportation parameters also vary for the same element with its speciation, e.g. partition to atmosphere or water. Organo-metallic cations (e.g. [Bu.sub.3][Sn.sup.+]) tend to be more water soluble and non-volatile, but saturated compounds (e.g. [(C[H.sub.3]).sub.4]Pb) are hydrophobic and volatile.

Additionally, a generation ago analytical chemists had generally to accept quantitative limits for their work of parts per thousand (ppt or mg [g.sup.-1]) e.g. for arsenic in a matrix (containing medium). At the time of the first edition of the present work (1986) parts per million or billion (ppm, ppb or µg [g.sup.-1], ng [g.sup.-1]) were being achieved. The standard now is commonly ppb (or ng [g.sup.-1]; the quantity present in [10.sup.9] parts of the matrix), but parts per [10.sup.-12] (ppt or pico grams per gram (fg [g.sup.-1])) are now commonly reported. It should always be borne in mind how relevant in practical terms such extreme measures of dilution might be, and analytical and environmental chemists should pause on occasion to consider which chemical species may not be present in a matrix at fg [g.sup.-1] or more dilute levels. Chemical analysis is usually targeted towards the species of interest and much else present may be missed or ignored. The question is, 'if the level of a certain species is of the order of [10.sup.-12] parts per gram, does it matter and if so, to whom?'

The above considerations also bring forward another point of terminology. Laboratory chemists usually express concentrations in molar terms, i.e. mot [dm.sup.-3]. At greater levels of dilution parts per million (ppm) and similar terms are often used. These terms are less precise, often because the matrix in which the species of interest is present is not water or a similar solvent. It is often a wet, amorphous sediment. Hence 'ppm' can mean one of the following:

(i) grams of the relevant atom present in [10.sup.6] grams of the matrix,

(ii) grams of a defined part of the molecule in [10.sup.6] grams of the matrix,

(iii) grams of the whole molecule in [10.sup.6] grams of the matrix.

In some published work, 'ppm' is not even defined as above. To add to the imprecision, the matrix (which may be a sediment or biological tissue) may be taken as wet (heavier) or dried (lighter)-giving two possible figures for the same measurement. Clarity of definition is not always present in quantitative work in this field, and the matrix is rarely the simple defined volume of known solvent that occurs in laboratory chemistry.

With regard to atmospheric or liquid measurements, terms such as ppm could mean:

(i) grams of the molecule (or relevant atom) present in [10.sup.6] [cm.sup.3] of atmosphere (at STP?) or water, or

(ii) volume ([cm.sup.3]) of the molecule (or relevant atom) present in [10.sup.6] [cm.sup.3] of atmosphere or water.

Care therefore needs to be taken when results from different laboratories or groups are compared. Consistency is often absent (even orthodox molar concentrations are sometimes used, even at extremes of dilution).

To put this field into perspective-although ppm, ppb and similar concentrations can be of major physiological, toxicological or environmental significance, it will do little harm to repeat the comparison given in the first edition of this work-a ppm is equivalent to a needle in a haystack; a ppb is equivalent to a grain of sand in an Olympic-sized swimming pool (in checking the calculation the reader is also invited to consider this as a not completely outlandish example of the use of imprecise concepts to register concentrations).

Within the present work, full standardization of terms is not possible owing to wide differences in practice, methods, matrices and analytical feasibility. To overcome this as far as possible, a basic attempt at standardization has been made and cross-referencing will then be used to clarify detailed points.

1.3 TYPES OF ORGANOMETALLIC COMPOUND

Most, but not all, organometallic compounds of environmental interest are covalent, bound by a u bond from a single carbon atom, to a main group element. The term 'organometallic' is generally defined as a compound with a bond (M-C) polarized [M.sup.[delta]+]-[C.sup.[delta]-] i.e. the metal is less electronegative than carbon. A compound containing carbon atoms, but where the bonds to the metal are not directly to the carbon atom (but may be via oxygen, nitrogen or halogen atoms instead), is not considered to be organometallic, although such a compound may be referred to as 'metal organic'.

Continues...


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Table of Contents

List of Contributors.

Preface.

Occurrence and Pathways of Organometallic Compounds in theEnvironment—General Considerations (P. J. Craig, etal.).

Organomercury Compounds in the Environment (R. Mason &J. Benoit).

Organotin Compounds in the Environment (F. Cima, et al.).

Organolead Compounds in the Environment (J. Yoshinaga).

Organoarsenic Compounds in the Marine Environment (J. Edmonds,et al.).

Organoarsenic Compounds in the Terrestrial Environment (D.Kuehnelt & W. Goessler).

Organoantimony Compounds in the Environment (P.Andrewes & W. Cullen).

Organosilicon Compounds in the Environment (A. Hirner, etal.).

Other Organometallic Compounds in the Environment (J.Feldmann).

Organoselenium Compounds in the Environment (P. Craig &W. Maher).

Some Standard Reference Sources on Organometallic andEnvironmental Organometallic Chemistry.

Index.

What People are Saying About This

From the Publisher

"This completely revised and updated edition treats environmental organometallic chemistry as an integrated and coherent subject area in its own right." (International Journal of Environmental Analytical Chemistry, Vol.84, No.14 – 15, 10 – 20 December 2004)

“…it is as a ‘one-stop-source’ of research information that this book should be most highly recommended”. ((Applied Organometallic Chemistry, March 2005)

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