What is the reason for the odd vowel values of Japanese ココア?


I've done a bit of digging, and for the life of me, I cannot find any clear
record or explanation for why Japanese ココア is pronounced the way it is.

Sources researched to date:

  * Lots of different sources at [the Kotobank entry for ココア](https://kotobank.jp/word/%E3%82%B3%E3%82%B3%E3%82%A2-64514), including Britannica Japan, Daijisen, Kokugo Dai Jiten, MyPedia, Chocolate / Cocoa Dictionary, etc etc.
  * Lots of different sources at [the Kotobank entry for カカオ](https://kotobank.jp/word/%E3%82%AB%E3%82%AB%E3%82%AA-43283)
  * [Chocolate & Cocoa Association of Japan's site](http://www.chocolate-cocoa.com/dictionary/history/japan/j01_a.html)
  * [Snippets from the journal of Tokugawa Akitake](https://books.google.com/books?id=pQc0AQAAIAAJ&dq=%22%E5%BE%B3%E5%B7%9D%E6%98%AD%E6%AD%A6%E5%B9%95%E6%9C%AB%E6%BB%9E%E6%AC%A7%E6%97%A5%E8%A8%98%22&focus=searchwithinvolume&q=%E3%82%B3%E3%82%B3%E3%82%A2) (1853–1910), listed as a source on the Chocolate & Cocoa Association's page, wherein Akitake described drinking ココア one morning when visiting the Paris World Fair in 1868, as listed also in [the Japanese Wikipedia article about him](https://ja.wikipedia.org/wiki/%E5%BE%B3%E5%B7%9D%E6%98%AD%E6%AD%A6#%E8%A8%AA%E6%AC%A7%E4%BD%BF%E7%AF%80%E5%9B%A3)

Lots of information is out there about カカオ and ココア, and what each of them are,
and how the former is turned into the latter. I can confirm in various sources
that カカオ is borrowed from Spanish, and ココア is borrowed from English. But I can
find nothing about why ココア is pronounced as //ko.ko.a//.

My suspicion is that this is the result of "book pronunciation", based on the
English spelling _cocoa_ and simply reading it out vowel-for-vowel. A distant
alternative possibility is that the Japanese word somehow metathesized the
vowels after borrowing _cacao_ , the common term for this in many other
European languages, including the Japanese-contact trifecta of Dutch, Spanish,
and Portuguese. English wound up with a pronunciation of //ˈkoʊ.koʊ// (US) or
//ˈkəʊ.kəʊ// (UK) not through any metathesis, but rather through early
confusion with _coco_ (as in _coconut_ ), as best I can tell. (See also [the
Wiktionary entry](https://en.wiktionary.org/wiki/cocoa#English).) If ココア were
borrowed from spoken English, we'd expect something more like //kóꜜò.kòò//,
instead of the //kóꜜ.kò.à// and //kó.kóꜜ.à// pronunciations evident in modern
usage.

Does anyone have any solid evidence for why we have this unexpected word form?
Or any leads on academics or references that discuss this oddity of etymology?




I don't have a conclusive case, but it seems like ココア was considered wrong at
some point. If it was an accidental mistake that stuck, there might not be a
very logical explanation.

Some old sources say ココア is a mistaken term with warped pronunciation (訛り),
maintaining that コーコー is more correct.

  * [「コーコー」は坊間にて「ココア」と誤稱する興奮性飮料の一なり](https://lab.ndl.go.jp/dl/book/1082673?keyword=%E3%82%B3%E3%82%B3%E3%82%A2,%E3%82%B3%E3%83%BC%E3%82%B3%E3%83%BC&page=63)
  * [從來我邦では訛つてココアと呼んで來たが近年統計類にコーコーと改めるやうになつた](https://lab.ndl.go.jp/dl/book/1029523?keyword=%E3%82%B3%E3%82%B3%E3%82%A2&page=32)
  * [ココア（コーコーの訛りだ）](https://lab.ndl.go.jp/dl/book/888202?keyword=%E3%82%B3%E3%82%B3%E3%82%A2,%E3%82%B3%E3%83%BC%E3%82%B3%E3%83%BC&page=45)

