Selenoxide Synthesis Essay

The first publication on the use of selenium(IV) oxide in oxidation reactions appeared in 1932 [27] and since then it has been applied as a versatile reagent for the synthesis of various types of organic compounds [12,23,24,25,28,29,30]. Due to its toxicity when taken orally, intense local irritation of skin and eyes, and the sometimes malodorous volatile selenium-containing by-products are formed, SeO2 is used in modern synthesis only when it competes favourably with other methods, provides unique reactivity or when it is used in catalytic amounts [1,2,4,12,24,25,26,27,29,30,31,32]. The TBHP/SeO2 or H2O2/SeO2 systems are more convenient to use than SeO2 alone, particularly when it is used in catalytic amounts, very often in 5 mol %. Reaction conditions are much milder and as a result, yields are higher with less oxidation, dehydration and rearrangement by-products. Moreover the problem of the removal of colloidal selenium is circumvented.

2.1. Allylic Hydroxylation

Selenium(IV) oxide-mediated oxidation of substituted olefins (Riley oxidation) is regarded as one of the most reliable and predictable methods for introducing a hydroxy group into the allylic position. The reaction reveals a very useful regio- and stereoselectivity when applied to trisubstituted olefins, producing predominantly (E)-allylic alcohols.

Selenium(IV) oxide mediates the unique allylic oxidation of alkenes 9 with usual retention of the double bond position. The mechanism of this reaction remained unclear until Sharpless and Lauer in 1972 [33] explained the selective oxidation as the result of a two-step process: an ene reaction followed by sigmatropic [2,3]-rearrangement of intermediate selenic(IV) acid 10 that give selenic(II) acid ester 11, while the double bond returns to its original location. In the last step the ester is hydrolyzed into the allylic alcohol 12 (Scheme 2). It was postulated that in the presence of a hydroxylated solvent, e.g., water, alcohol or a carboxylic acid, the active oxidant could be selenic(IV) acid or its alkyl ester.

Scheme 2. Mechanism of selenium(IV) oxide α-hydroxyalkylation of alkenes.

Scheme 2. Mechanism of selenium(IV) oxide α-hydroxyalkylation of alkenes.

A comparison of the observed 13C and 2H kinetic isotope effects with the predicted values shows that the observed effects are consistent with an initial concerted ene reaction step mediated by SeO2. However, this comparison does not rule out the involvement of a selenic(IV) ester in the ene reaction or a stepwise reaction involving reversible electrophilic addition of HSeO2+ followed by a rate-limiting proton abstraction. B3LYP calculations strongly favour SeO2 over a selenic(IV) ester as the active oxidant, with a predicted barrier of 21–24 kcal·mol−1 lower for the reaction of 2-methyl-3-butene with SeO2 than that for the reaction with H2SeO3. The possibility of a selenic(IV) ester as the active oxidant is also disfavoured by the observation of oxidations in non-hydrolytic solvents. A concerted ene reaction with SeO2 as the active oxidant thus appears to be the major mechanistic pathway in these reactions [34,35,36].

Selenium(IV) oxide allylic hydroxylations are highly regiospecific and occur at the α-position to the more substituted carbon of the double bond with a reactivity order CH2 > CH3 > CH. When the double bond is inside a ring, oxidation occurs in the ring when possible, and in the α-position to the more substituted end of the double bond. Another synthetically very useful aspect in this conversion of the nonactivated C=C double bond into the allylic alcohol intermediate lies in its high stereoselectivity, as demonstrated in the oxidation of 1-tert-butyl-4-alkylidenecyclohexanes [36].

The (Z)-selective allylic alcohol formation of dialkyl alkylidenesuccinates induced by SeO2 has been demonstrated to accomplish one-step syntheses of several essential and fused butenolides via an unusual E- to Z- carbon-carbon double bond isomerization followed by lactonization pathway. The observed regio- and stereoselective SeO2 allylic oxidation protocol has also been extended to the diastereoselective total synthesis of the bioactive natural product isomint lactone, its direct conversion to mint lactone and an example of the base-catalyzed intramolecular rearrangement of γ-lactone to δ-lactone. As depicted in Scheme 3, the initial expectation was that the regioselective SeO2 allylic oxidation of (E)-dimethyl 2-propylidenesuccinate 13 would provide (E)-dimethyl 2-propylidene-3-hydroxysuccinate 15 or pyran skeleton 16. The allylic oxidation of compound 13, in the presence of a catalytic amount of SeO2 and tert-butyl hydroperoxide in tert-butyl alcohol/1,4-dioxane at room temperature, was not successful and the starting material remained unreacted. When the compound 13 was treated with SeO2 (1.60 equiv) in refluxing 1,4-dioxane, the allylic oxidation reaction was completely regioselective and provided the butenolide product 14. This suggested that in the SeO2-induced transformation of dimethyl (E)-2-propylidenesuccinate 13 to product 14, apart from allylic hydroxylation, the course of reaction involves a E- to Z- carbon–carbon double bond isomerization and an in situ intramolecular cyclization step [37].

Scheme 3. Regio- and stereoselective SeO2 oxidation of (E)-dimethyl 2-propylidenesuccinate 13.

Scheme 3. Regio- and stereoselective SeO2 oxidation of (E)-dimethyl 2-propylidenesuccinate 13.

Selenium dioxide was found to be a reliable reagent for the direct regioselective insertion of oxygen at the allylic carbon via α-hydroxylation. Various 1,3-diarylpropenes were oxidized with SeO2 in ethanol in 50%–58% yield. For example, the reaction of diarylpropene 17 with SeO2 in ethanol gave p′-methylchalcone 18 in 50% yield (Scheme 4) [38].

Scheme 4. Oxidation of diarylpropene to p′-methylchalcone.

Scheme 4. Oxidation of diarylpropene to p′-methylchalcone.

Selenium(IV) dioxide is still used for allylic hydroxylation in several multistep syntheses and transformations of natural products, their precursors and analogues such as 6-hydrocorticosteroids, 6-β-hydroxy derivatives of progesterone and testosterone, glycospirostanes, the optically pure cyclohexenone core scyphostatin and hydroxytaxadienes [39,40,41,42,43,44,45]. Allylic oxidation of phlomisoic acid and its methyl ester by selenium(IV) dioxide occurred stereoselectively to form α-hydroxy derivatives of labdanoids [46].

Like selenium(IV) oxide alone, the reagent TBHP/SeO2 oxidizes alkenes, cycloalkenes and alkynes in the allylic position. Hydroxylation of cycloalkenes carrying alkyl substituents at the allylic position, takes place preferentially on the ring α-carbon atom. Oxidation of terminal alkenes results in C=C bond migration and primary allyl alcohols formation. Terminal and non-terminal vinyl fluorides have been hydroxylated regioselectively in the allylic and propargylic position adjacent to the fluorine-bearing carbon [47].

TBHP/SeO2 was used in the allylic hydroxylation of isolated double bonds in straight-chain hydrocarbons, e.g., monounsaturated fatty acids, esters and alcohols. Either allylic position was hydroxylated or both positions reacted, to give dihydroxy isomers. Yields of monohydroxy compounds in which the OH group was between the double bond and C(1), were usually higher than those in which the OH group was between the double bond and the methyl terminus. When an α-methylene group is oxidized, the reaction proceeds under mild reaction conditions [1,2,9,17,43,48]. For example, TBHP/SeO2 oxidation of compound 19 in multistep synthesis of (−)-okilactomycin gave both possible isomers 20 and 21 (Scheme 5) [49]. A mixture of taxadienes (87% of taxa-4(5),11(12)-diene and 13% of taxa-4(20),11(12)-diene), was subjected to oxidation with TBHP/SeO2 and stoichiometric amounts of selenium(IV) oxide. In both cases, the expected α-hydroxylation products were isolated [50].

Scheme 5. Allylic TBHP/SeO2 oxidation in the total synthesis of (−)-okilactomycin.

Scheme 5. Allylic TBHP/SeO2

The word “synthesis” is defined as a combination of elements to form a connected whole. Thus, a synthesis essay definition is an essay that combines different ideas into a whole to prove a point (otherwise called the thesis). Often, it comes with a text that you should analyze.


Table Of Contents


Writing Process

A key factor of writing a synthesis essay is an analysis of a given text or a prompt. In order to successfully analyze it, you must comprehend the text’s purpose, rhetoric, and the argument that the author’s claim, in other words, you are answering the question: “So what?”. Then, you must build your own claim, and write an essay around that.

Most Common Topics

A synthesis essay prompt must be negotiable. Like in the EssayPro's example above, Andrew Jackson’s negative views on Native American people were widely supported, today, however, they would be appalling. Depending on your assignment, you may have to choose a primary text. Choose a text that might have opposing viewpoints.

Good topics would be ones that are debatable, for example:

  • Daylight savings
  • Minimum wage
  • Abortion
  • Immigration policy
  • Global warming
  • Gun control
  • Social media

How Do I Write A Thesis?

Once you pick a topic of your paper, read your sources and establish your position. Make sure you thoroughly analyze the sources and get a good understanding of them, structure your claim or argument and write your thesis.

Example: Andrew Jackson’s fear of the Native American “savages” reflects the prejudices and ideas of the colonist people in the Union and the Congress.*

How Do I Write An Outline?

Creating an outline will help maintain the structure of your paper. If your essay is split into three parts, split your outline into three chunks. Paste supporting evidence, sub-arguments, and specific points in the appropriate sections. Make sure that every point somehow proves the claim in your thesis. Extra information or tangents will only hinder your essay. However, if information goes against your central claim, then you should acknowledge it as it will make your essay stronger. Make sure you have read all of your sources. When writing about the sources, do not summarize them; synthesis denotes analysis, not plot-summary.

Example:

  • Introduction
  • Thesis
    • Main point 1
    • Main point 2
    • Main point 3
  • Body
  • Main point 1
    • Evidence (quote from a source)
    • Analysis of Evidence
  • Main point 2
    • Evidence (quote from a source)
    • Analysis of Evidence
  • Main point 3
    • Evidence (quote from a source)
    • Analysis of Evidence
  • Conclusion
  • Restate main points and answer unanswered questions

Read more about how to write a great INTRODUCTION

How Do I Format My Essay?

The format depends on what style is required by your teacher or professor. The most common formats are: MLA, APA, and Chicago style. APA is used by fields of Education, Psychology, and Science. MLA is used for citing Humanities, and Chicago style is used for Business, History, and Fine Arts. Purdue Owl is a format guide that focuses mainly on MLA and APA, and Easybib is a citation multitool for any of your external sources.

Some key points are:

  • Times New Roman 12 pt font double spaced
  • 1” margins
  • Top right includes last name and page number on every page
  • Titles are centered
  • The header should include your name, your professor’s name, course number and the date (dd/mm/yy)
  • The last page includes a Works Cited

APA Format

Some key points are:

  • Times New Roman 12 pt font double spaced 1” margins
  • Include a page header on the top of every page
  • Insert page number on the right
  • An essay should be divided into four parts: Title Page, Abstract, Main Body, and References.

How do I write an AP English Synthesis Essay?

AP English Language and Composition is an extremely rigorous course that requires you to write essays that demonstrate deep understanding of the subject matter. In fact, if on the AP exam, your essay has perfect grammar and structure, you might still be awarded just 1 out of 9 points for not “defending, challenging, or qualifying your claim.” Sounds difficult, but it is doable. Before entering any AP class, it is best to read over the course overview and become familiar with the exam.

While writing, focus on the three branches of the AP English and Composition course: argument, synthesis, and rhetorical analysis.

Argument is the easiest component; create your claim and find specific supporting evidence. Convince your reader that you are right.

Synthesis requires you to read into multiple perspectives and identify an agreement and a disagreement between sources. This step is crucial to finding your own claim.

Rhetorical analysis deals with the author and his intentions. What was their purpose for writing this? Who is their intended audience? How does the author appeal to the audience and how does he structure his claim?

Essay Tips

There are two acronyms that are helpful with the three AP Lang writing branches.

Tip #1: SOAPS

Example text: Andrew Jackson’s speech to the Congress about sending Native Americans to the West.

Speaker: Identify the speaker of the piece, then analyze for bias and apply any prior knowledge that you have on the speaker.

Example: President Andrew Jackson had a bias against Native Americans. A piece written by Andrew Jackson about Native Americans will probably be written with a bias against him.

Occasion: Determine the time and the place of the written text, then identify the reason the text was written. Even if you aren’t sure of the reason, assume one and make your claim around it.

Example: Andrew Jackson was in office from 1829 to 1837. At this time, the Congress sent Native Americans to the West in order to clear the land for the colonists. Jackson was the one who made the proposal.

Audience: Who was the text directed to?

Example: Andrew Jackson’s speech was directed to a council.

Purpose: What is the text trying to say? Here, you analyze the tone of the text.

Example: Andrew Jackson appeals to pathos by calling Indians “savages”. His purpose is to portray Native Americans in a negative light, so the Congress passes the Indian Removal Act.

Subject: What is the main idea? What is the claim?

Example: Andrew Jackson wants the Congress to pass the Indian Removal Act because he believes Native Americans are uncultured and savage people.

Tip #2: Logos, Ethos, and Pathos

As you’ve probably learned before, Logos appeals to reason, Pathos appeals to emotion, and Ethos appeals to moral philosophy or credibility. However, for the AP Lang exam requires a wider understanding of the three.

If the text uses facts, statistics, quotations, and definitions, the speaker is appealing to Logos. Constituting various backup information is an extremely effective for people who want to persuade.

If the text uses vivid imagery and strong language it denotes Pathos, which is used to connect the audience to a piece emotionally; it is hardest to change the mind of a person who is linked to a subject via a strong emotion.

If the text attempts to demonstrate the speakers reliability or credibility, it is a direct appeal to Ethos. Using the example above, Andrew Jackson could have appealed to Ethos by stating the fact that he is the President of the United States, and thus, knows what is best for the union.

Often, Logos, Ethos, and Pathos lead to the use of logical fallacies.

Tip #3: DIDLS

This is a good shorthand for all textual analysis. While reading a text, try to pinpoint Diction, Imagery, Details, Language, and Sentence Structure in a piece. If anything stands out, add it to your analysis.

Rubric

  • High range essay (8-9 points)
  • Effectively develops a position on the assigned topic.
  • Demonstrates full understanding of the sources or text.
  • Correctly synthesizes sources and develops a position. The writer drives the argument, not the sources.
  • The writer’s argument is convincing.
  • The writer makes no general assertions and cites specific evidence for each point. His/her evidence is developed and answers the “so what?” question.
  • The essay is clear, well-organized, and coherent. It is a stand alone piece rather than an exam response.
  • Contains very few grammatical and spelling errors or flaws, if any.

Note: 8-9 essays are an extreme rarity. A strong ‘7’ paper can jump to an 8-9 if the writing style is mature and perceptive.

Middle-Range Essay (57)

  • Adequately develops a position on the assigned topic.
  • Demonstrates sufficient understanding of the ideas developed in sources
  • Sufficiently summarizes the sources and assumes some control of the argument. ‘5’ essays are less focused than ‘6’ and ‘7’.
  • The writer's argument is sufficient but less developed.
  • Writer successfully synthesizes the sources and cites them.
  • Writer answers the “So what?” question but may use generalizations or assertions of universal truth. Writer cites own experience and specific evidence.
  • Essay is clear and well organized. ‘5’ essays less so.
  • Contains few minor errors of grammar or syntax.

Note: A ‘7’ is awarded to papers of college-level writing.
A ‘5’ on one of the AP English Language and Composition essays designates a 3 on the AP exam. It most likely relies on generalizations has limited control of the claim and argument. ‘5’ essays often lose focus and digress.

Low-Range Essays (1-4)

  • Inadequately develops a position on the assigned topic.
  • The author misunderstands and simplifies the ideas developed in the sources.
  • Over-summarizes the sources, lets the sources drive the argument.
  • Writer has weak control of organization and syntax. Essay contains numerous grammatical/spelling errors.
  • Writer does not cite the sources correctly, skips a citation, or cites fewer than the required minimum of the sources.
  • Notes: ‘4’ or ‘3’ essays do assert an argument but do not sufficiently develop it.
  • A ‘2’ essay does not develop an argument.
  • A 1-2 essay has severe writing errors and do not assert a claim.

Synthesis Essay Example

Essay Writing Advice From Our Professional Team

James Owen, online essay writer from EssayPro

The article reviews the basics of how to write a synthesis essay as well as how to dissect and analyze text when writing an AP English essay. One thing I would like to reemphasize is the importance of your thesis statement. When you write an essay for class or exam, make sure to state your argument clearly. If the reader of your essay doesn’t understand your point of view then what you’ve written is futile.

My advice is: when writing an essay in a short period (such as in an exam room) make sure to articulate your argument in every paragraph and connect every single one of your ideas to the thesis. My tip is to write your thesis down on a piece of paper and reread it at every point to ensure that the information applies and reinforces what you’ve stated in your thesis. This tip also goes for when you are writing a longer piece of writing, as it is very easy to lose focus and stray away from your main point.

Struggling With Writing an Essay?

Still having trouble crafting a synthesis essay? Need editing or writing help? You should seek advice from professional writers. Here at EssayPro, writers have written countless papers and are experts in their field. You can request to write your paper or editing or proofreading assistance. Rest assured that your paper is in good hands!

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