Reaction Green Metrics

Problems, Exercises, and Solutions

John Andraos

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9780429754418
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

This book contains a series of exercises and problems posed in the subject of green metrics. Essentially it is a "how to" book on evaluating the material efficiency, environmental impact, safety-hazard impact, and energy efficiency of any kind of chemical reaction or synthesis plan. Only the essential green metrics in each of these categories are used. The introduction highlights the hierarchy of metrics used throughout the book, explains the structure of how the book is arranged, how the problems are posed, and how the reader is to use the book. Examples refer to themes according to the headings given in the table of contents and are arranged in a hierarchical order.

Key Features:

• The topics cover fundamentals in chemistry and the chemical industry in a blended fashion
• A unique text covering the fundamentals of green metrics from materials efficiency and environmental and safety-hazard impact, to new green technologies and more
• The book will be useful in a range of chemistry courses, from early undergraduate to advanced graduate courses, whether based in lectures, tutorials or laboratory experiments
• Using an extensive glossary of terms used in green metrics, each chapter has a specified theme where the relevant metrics definitions pertaining to that theme will be given with one or two illustrative worked examples
• Supplemental web-based downloadable material including extra problems, full solutions, Excel files, ChemDraw files, templates, and exercises

1	Introduction

After 25 years of development, the field of green chemistry has reached critical crossroads on both the education and research fronts. With respect to educating the next generation of chemical scientists, interest in green chemistry is dominated by undergraduate instructors who mainly use it as a means to engage modern students who are active learners and who are seeking ways to make a difference in coming up with innovative solutions to address pressing world problems where science can have a positive impact. Despite this noble cause, green chemistry is still considered a “soft fringe subject” in physical science among research faculty in departments of chemistry as evidenced by the fact that green chemistry is not yet part of the mainstream curriculum for honors degree chemistry programs at leading universities and colleges. In the few places where it does get mentioned in the curriculum, either explicitly or implicitly, it is presented largely in a show-and-tell approach with little quantitative rigor.

In the few dedicated research journals such as Green Chemistry (Royal Society), ChemSusChem (Wiley-VCH), Green Chemistry Letters and Reviews (Taylor & Francis), and ACS Sustainable Chemical Engineering (American Chemical Society), which give a voice to cutting-edge research in the field, there are lingering issues. Again, most contributions are presented in a show-and-tell approach with little or no quantitative evidence that backs up the claims of “greenness” made in the research articles. If comparative metrics analysis were to be applied to such pronouncements, it would be readily found that few of them would uphold their claims of “greenness.” Up until now, there are no formalized standards put in place on the presentation of so-called green metrics that track any improvements made. Editors have largely left the task to authors’ discretion on a voluntary basis for application of metrics in research to justify the implementation of one or more green chemistry principles. Articles focused on metrics themselves, particularly in the areas of material efficiency and life cycle assessment (LCA), are often fraught with “me-too” metrics, where the same ideas are re-branded with new nomenclature depending on the authors, and are presented in a manner without head-to-head comparison of “new” algorithms with prior published algorithms and without framing the discussion in the context of performance, limitations, advantages, and disadvantages among the various methods.

From the point of view of process chemistry, there still exists the narrow-minded view that overall mass balance and inventory control encompasses all that is needed for applying green chemistry metrics when it comes to tracking input material consumption and waste material production. Essentially, metrics such as overall E-factor (mass of waste per unit mass of product) and overall PMI (mass of input materials per unit mass of product) are the main concerns—all other material efficiency metrics are considered unduly complicated and thus “over-engineer” the problem of optimization. Of course, this simple approach does not require knowledge of chemistry and only relies on elementary accounting of what goes in versus what comes out of a process. A non-chemistry professional can adequately perform such a task. In doing so, there is little attention paid to making the connection to individual reaction step performances of these metrics and how they relate to the overall metrics for an entire process. When that connection is made, suddenly it becomes apparent that one needs to know the chemistry of each reaction step before waste minimization can begin.

The order of steps undertaken in optimizing a synthesis is also problematic. Solvent reduction and elimination is a top priority since it is obvious that these materials constitute the bulk of input materials used in a chemical process. This is the first line of attack in “greening up” an existing chemical process. However, less attention is paid to inventing new reactions that do not produce by-products from the outset. Coming up with such high atom economy reactions requires imagination. This takes more time and effort. With respect to reducing toxicity and hazard issues, the focus is again on solvents via solvent replacement to arguably more benign ones. The task of synthesis optimization is often carried out in a multi-pronged attack where material metrics, commercial cost and availability, and LCA are optimized simultaneously rather in a structured or layered approach. This leads to a jumble with respect to ranking plans where the inevitable outcome is non-orchestrated optimization. Energy metrics are essentially excluded from experimental procedures and therefore from the discussion of reaction and synthesis optimization.

1.1 What This Book Is About

This book addresses the aforementioned problems described in education and research with a focus on material efficiency assessment of individual reactions. In order to successfully navigate the topics presented, the reader is expected to have adequate background knowledge in the following subjects as necessary prerequisites. In chemistry, the reader should have already taken an introductory organic chemistry course, has familiarity with reaction mechanism, has a basic library of named organic reactions committed to memory, and is familiar with drawing and interpreting catalytic cycles. Most importantly, balancing chemical equations is highly emphasized. This skill will be the most challenging to master for a student or a professional, but is a mandatory starting point for solving every example and question posed in this book. No metrics analysis of any kind can begin without first establishing a balanced chemical equation for a given chemical transformation. Time and space are devoted to the following new topics not covered or mentioned in standard undergraduate chemistry courses: (a) drawing schemes for reactions and synthesis plans using the principle of conservation of structural aspect as a key strategy for in-depth understanding and analysis of synthesis strategy and its quantitative parameterization; and (b) connecting balanced chemical equations with their reaction mechanisms. Since this book combines chemistry with quantitative reasoning, there are certain topics in mathematical science that the reader is expected to be fluent in. Specifically, these include basic arithmetic and basic algebra. In order for the reader to take full advantage of the accompanying online suite of spreadsheet algorithms available for Instructors to download by request at https://www.crcpress.com/9781138388949, mastery of Microsoft Excel spreadsheet software and facility with graphing are highly recommended. These spreadsheets and calculators were designed to remove the tedious task of computing metrics by hand. In addition, extensive databases of key physical and toxicological properties of commonly used industrial chemicals are given in one place so the reader does not have to scour the literature to find them, thereby speeding up the process of conducting calculations and interpreting the results of those calculations.

1.2 Structure

The topics in this book are presented in a ladder approach where each successive topic follows logically from the previous one. Chapter 2 begins with understanding how to parse the identities and roles of input materials used in a chemical reaction and how to balance chemical equations. Specific attention is paid to redox (reduction-oxidation) reactions because they are the most challenging to balance and yet figure prominently in industrial and process chemistry. Chapter 3 discusses the variety of presentations of experimental procedures appearing in the chemistry literature and how their quality impacts the definiteness of any metrics analysis that is possible. Chapter 4 summarizes the types of chemical reactions that are possible and introduces a standardized nomenclature to describe ring construction strategies. Chapter 5 is an important chapter that is devoted to the principle of conservation of structural aspect and its impact on parameterizing and analyzing synthesis strategy. Standards for the presentation of reaction mechanisms, target bond mapping, and tracking oxidation states in bond forming steps in a synthesis plan are introduced. Chapter 6 introduces metrics that are specific to waste production and input material consumption applied to individual chemical reactions. This chapter focuses on the essential metrics and excludes all superfluous “me-too” metrics that are present in the literature. Most importantly, the selected metrics are connected in a structured and logical hierarchy for immediate comprehension and usage. Chapter 7 is devoted to the concepts of intrinsic greenness and minimum atom economy, and assessing the probability that a given chemical reaction will achieve intrinsic greenness subject to minimum atom economy and reaction yield constraints. An extensive inventory of the library of organic reactions is presented to showcase the present state of the art. Chapter 8 is devoted to presenting all of the Microsoft Excel spreadsheets that have been developed to evaluate material efficiency of individual reactions and synthesis plans in an automated, reliable, and easy-to-use fashion.

1.3 How to Use the Book

For teaching purposes, instructors can use the worked examples in a classroom setting to introduce topics for discussion in lectures and the problems as homework set exercises for deeper thought. It is recommended that the book be used in a one-semester introductory course on green chemistry as a dedicated subject spanning academic and industrial chemistry topics. The style of presentation is brief where definitions of terms are presented first along with an immediate easy example. Each topic is briefly introduced followed by worked examples to illustrate the ideas for immediate understanding and implementation. Advanced problems are posed at the conclusion of each chapter. Consistent with good pedagogy, all examples and problems posed come directly from literature sources, which are cited upfront for both instructors and students to view. Solutions to all problems are available electronically through the publisher’s website.

For research purposes, experienced readers may skip topics they are familiar with and focus on those areas they wish to learn more about as needed. The same pedagogical style described above is applicable to experienced chemists for their benefit. Examples and problems of interest to industrial chemists, process chemists, and chemical engineers have been taken from both research journals and patents.

2	Constitution of a Chemical Reaction and Reaction Balancing

2.1 Identifying Components of any Chemical Reaction

2.1.1 Terms, Definitions, and Examples

Additive

A substance added to a reaction mixture that improves reaction performance toward a desired product but whose role is not well defined.

_Auxiliary

A substance or material used in the post-processing of a chemical reaction typically in work-up procedures involving washing or extraction and in purification procedures involving chromatography or recrystallization.

By-Product [1, 2]

A product formed in a reaction between reagents as a direct mechanistic consequence of producing the target product assuming a balanced chemical equation that accounts for the production of that target product. By-products and the target product appear on the right-hand ...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Dedication
• Contents
• Preface
• Chapter 1 Introduction
• Chapter 2 Constitution of a Chemical Reaction and Reaction Balancing
• Chapter 3 Experimental Description of Chemical Reactions
• Chapter 4 Chemical Reaction Classifications
• Chapter 5 Drawing Chemical Structures
• Chapter 6 Waste Production and Input Material Consumption
• Chapter 7 Intrinsic Greenness
• Chapter 8 Automated Computation for a Single Reaction
• Appendix: Other Terminologies
• Index